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 $54.38   8.484%   $58.9936   $58.99   $59.00   $59.00  
  Purchase #2 $228.59   4.205%   $238.2022   $238.20   $238.20   $238.20  
  Purchase #3 $151.88   13.863%   $172.9351   $172.94   $172.95   $172.90  
  Purchase #4 $197.36   10.733%   $218.5426   $218.54   $218.55   $218.50  
  Purchase #5 $129.30   11.746%   $144.4876   $144.49   $144.50   $144.50  
  Purchase #6 $15.66   7.294%   $16.8022   $16.80   $16.80   $16.80  
  Purchase #7 $87.82   11.155%   $97.6163   $97.62   $97.60   $97.60  
  7 purchase totals = $864.99       $947.5796   $947.58   $947.60   $947.50