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 $64.30   8.548%   $69.7964   $69.80   $69.80   $69.80  
  Purchase #2 $216.85   4.711%   $227.0658   $227.07   $227.05   $227.10  
  Purchase #3 $142.78   7.813%   $153.9354   $153.94   $153.95   $153.90  
  Purchase #4 $29.94   3.406%   $30.9598   $30.96   $30.95   $31.00  
  Purchase #5 $245.40   11.674%   $274.048   $274.05   $274.05   $274.00  
  Purchase #6 $234.57   7.747%   $252.7421   $252.74   $252.75   $252.70  
  Purchase #7 $225.90   5.485%   $238.2906   $238.29   $238.30   $238.30  
  7 purchase totals = $1,159.74       $1,246.8381   $1,246.85   $1,246.85   $1,246.80