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 $221.79   11.462%   $247.2116   $247.21   $247.20   $247.20  
  Purchase #2 $94.31   10.314%   $104.0371   $104.04   $104.05   $104.00  
  Purchase #3 $185.62   8.240%   $200.9151   $200.92   $200.90   $200.90  
  Purchase #4 $201.86   11.378%   $224.8276   $224.83   $224.85   $224.80  
  Purchase #5 $85.70   9.329%   $93.695   $93.70   $93.70   $93.70  
  Purchase #6 $32.82   13.621%   $37.2904   $37.29   $37.30   $37.30  
  Purchase #7 $45.96   4.661%   $48.1022   $48.10   $48.10   $48.10  
  7 purchase totals = $868.06       $956.0790   $956.09   $956.10   $956.00