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 $203.87   12.208%   $228.7584   $228.76   $228.75   $228.80  
  Purchase #2 $153.64   10.115%   $169.1807   $169.18   $169.20   $169.20  
  Purchase #3 $80.64   5.491%   $85.0679   $85.07   $85.05   $85.10  
  Purchase #4 $86.34   11.816%   $96.5419   $96.54   $96.55   $96.50  
  Purchase #5 $168.97   8.776%   $183.7988   $183.80   $183.80   $183.80  
  Purchase #6 $67.34   5.312%   $70.9171   $70.92   $70.90   $70.90  
  Purchase #7 $93.48   5.145%   $98.2895   $98.29   $98.30   $98.30  
  7 purchase totals = $854.28       $932.5543   $932.56   $932.55   $932.60