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 $62.37   7.425%   $67.001   $67.00   $67.00   $67.00  
  Purchase #2 $122.29   9.635%   $134.0726   $134.07   $134.05   $134.10  
  Purchase #3 $97.97   13.703%   $111.3948   $111.39   $111.40   $111.40  
  Purchase #4 $231.71   10.476%   $255.9839   $255.98   $256.00   $256.00  
  Purchase #5 $104.99   8.234%   $113.6349   $113.63   $113.65   $113.60  
  Purchase #6 $208.32   3.792%   $216.2195   $216.22   $216.20   $216.20  
  Purchase #7 $64.98   5.105%   $68.2972   $68.30   $68.30   $68.30  
  7 purchase totals = $892.63       $966.6039   $966.59   $966.60   $966.60