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 $33.26   12.145%   $37.2994   $37.30   $37.30   $37.30  
  Purchase #2 $66.95   11.802%   $74.8514   $74.85   $74.85   $74.90  
  Purchase #3 $237.53   12.163%   $266.4208   $266.42   $266.40   $266.40  
  Purchase #4 $10.48   4.613%   $10.9634   $10.96   $10.95   $11.00  
  Purchase #5 $140.40   6.122%   $148.9953   $149.00   $149.00   $149.00  
  Purchase #6 $24.83   4.555%   $25.961   $25.96   $25.95   $26.00  
  Purchase #7 $239.54   8.810%   $260.6435   $260.64   $260.65   $260.60  
  7 purchase totals = $752.99       $825.1348   $825.13   $825.10   $825.20