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 $47.81   11.198%   $53.1638   $53.16   $53.15   $53.20  
  Purchase #2 $67.42   12.113%   $75.5866   $75.59   $75.60   $75.60  
  Purchase #3 $144.87   4.732%   $151.7252   $151.73   $151.75   $151.70  
  Purchase #4 $198.60   10.823%   $220.0945   $220.09   $220.10   $220.10  
  Purchase #5 $95.39   7.245%   $102.301   $102.30   $102.30   $102.30  
  Purchase #6 $128.78   9.353%   $140.8248   $140.82   $140.80   $140.80  
  Purchase #7 $182.99   10.554%   $202.3028   $202.30   $202.30   $202.30  
  7 purchase totals = $865.86       $945.9987   $945.99   $946.00   $946.00