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 $144.53   8.451%   $156.7442   $156.74   $156.75   $156.70  
  Purchase #2 $88.35   7.476%   $94.955   $94.96   $94.95   $95.00  
  Purchase #3 $46.46   5.368%   $48.954   $48.95   $48.95   $49.00  
  Purchase #4 $121.68   6.816%   $129.9737   $129.97   $129.95   $130.00  
  Purchase #5 $62.48   4.510%   $65.2978   $65.30   $65.30   $65.30  
  Purchase #6 $225.37   7.664%   $242.6424   $242.64   $242.65   $242.60  
  Purchase #7 $112.47   11.508%   $125.413   $125.41   $125.40   $125.40  
  7 purchase totals = $801.34       $863.9801   $863.97   $863.95   $864.00