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 $64.79   13.188%   $73.3345   $73.33   $73.35   $73.30  
  Purchase #2 $246.35   5.661%   $260.2959   $260.30   $260.30   $260.30  
  Purchase #3 $57.50   5.105%   $60.4354   $60.44   $60.45   $60.40  
  Purchase #4 $182.88   8.209%   $197.8926   $197.89   $197.90   $197.90  
  Purchase #5 $200.70   8.619%   $217.9983   $218.00   $218.00   $218.00  
  Purchase #6 $59.39   9.190%   $64.8479   $64.85   $64.85   $64.80  
  Purchase #7 $55.68   4.599%   $58.2407   $58.24   $58.25   $58.20  
  7 purchase totals = $867.29       $933.0453   $933.05   $933.10   $932.90