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 $188.60   6.756%   $201.3418   $201.34   $201.35   $201.30  
  Purchase #2 $182.93   7.420%   $196.5034   $196.50   $196.50   $196.50  
  Purchase #3 $46.83   13.514%   $53.1586   $53.16   $53.15   $53.20  
  Purchase #4 $86.46   11.763%   $96.6303   $96.63   $96.65   $96.60  
  Purchase #5 $102.97   7.656%   $110.8534   $110.85   $110.85   $110.90  
  Purchase #6 $73.25   4.388%   $76.4642   $76.46   $76.45   $76.50  
  Purchase #7 $160.75   4.185%   $167.4774   $167.48   $167.50   $167.50  
  7 purchase totals = $841.79       $902.4291   $902.42   $902.45   $902.50