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 $67.49   8.415%   $73.1693   $73.17   $73.15   $73.20  
  Purchase #2 $150.42   4.140%   $156.6474   $156.65   $156.65   $156.60  
  Purchase #3 $99.45   5.776%   $105.1942   $105.19   $105.20   $105.20  
  Purchase #4 $137.70   4.415%   $143.7795   $143.78   $143.80   $143.80  
  Purchase #5 $149.82   13.125%   $169.4839   $169.48   $169.50   $169.50  
  Purchase #6 $170.75   13.352%   $193.5485   $193.55   $193.55   $193.50  
  Purchase #7 $126.32   9.342%   $138.1208   $138.12   $138.10   $138.10  
  7 purchase totals = $901.95       $979.9436   $979.94   $979.95   $979.90