Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.77   10.227%   $169.4961   $169.50   $169.50   $169.50  
  Purchase #2 $168.89   3.531%   $174.8535   $174.85   $174.85   $174.90  
  Purchase #3 $161.53   12.687%   $182.0233   $182.02   $182.00   $182.00  
  Purchase #4 $154.57   11.754%   $172.7382   $172.74   $172.75   $172.70  
  Purchase #5 $202.96   5.188%   $213.4896   $213.49   $213.50   $213.50  
  Purchase #6 $122.57   13.810%   $139.4969   $139.50   $139.50   $139.50  
  Purchase #7 $226.35   12.636%   $254.9516   $254.95   $254.95   $255.00  
  7 purchase totals = $1,190.64       $1,307.0492   $1,307.05   $1,307.05   $1,307.10