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 $196.69   8.262%   $212.9405   $212.94   $212.95   $212.90  
  Purchase #2 $60.78   4.137%   $63.2945   $63.29   $63.30   $63.30  
  Purchase #3 $166.94   7.442%   $179.3637   $179.36   $179.35   $179.40  
  Purchase #4 $66.54   10.479%   $73.5127   $73.51   $73.50   $73.50  
  Purchase #5 $125.56   7.775%   $135.3223   $135.32   $135.30   $135.30  
  Purchase #6 $42.30   6.105%   $44.8824   $44.88   $44.90   $44.90  
  Purchase #7 $14.61   4.858%   $15.3198   $15.32   $15.30   $15.30  
  7 purchase totals = $673.42       $724.6359   $724.62   $724.60   $724.60