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 $117.76   5.857%   $124.6572   $124.66   $124.65   $124.70  
  Purchase #2 $133.79   11.520%   $149.2026   $149.20   $149.20   $149.20  
  Purchase #3 $136.75   8.567%   $148.4654   $148.47   $148.45   $148.50  
  Purchase #4 $242.94   5.204%   $255.5826   $255.58   $255.60   $255.60  
  Purchase #5 $112.93   11.526%   $125.9463   $125.95   $125.95   $125.90  
  Purchase #6 $98.82   3.779%   $102.5544   $102.55   $102.55   $102.60  
  Purchase #7 $56.25   11.179%   $62.5382   $62.54   $62.55   $62.50  
  7 purchase totals = $899.24       $968.9467   $968.95   $968.95   $969.00