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 $92.59   11.590%   $103.3212   $103.32   $103.30   $103.30  
  Purchase #2 $162.65   11.696%   $181.6735   $181.67   $181.65   $181.70  
  Purchase #3 $243.45   5.869%   $257.7381   $257.74   $257.75   $257.70  
  Purchase #4 $82.40   11.162%   $91.5975   $91.60   $91.60   $91.60  
  Purchase #5 $7.48   13.823%   $8.514   $8.51   $8.50   $8.50  
  Purchase #6 $78.49   7.613%   $84.4654   $84.47   $84.45   $84.50  
  Purchase #7 $168.69   8.252%   $182.6103   $182.61   $182.60   $182.60  
  7 purchase totals = $835.75       $909.9200   $909.92   $909.85   $909.90