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 $216.86   8.361%   $234.9917   $234.99   $235.00   $235.00  
  Purchase #2 $105.94   6.241%   $112.5517   $112.55   $112.55   $112.60  
  Purchase #3 $68.73   6.571%   $73.2462   $73.25   $73.25   $73.20  
  Purchase #4 $246.62   11.250%   $274.3648   $274.36   $274.35   $274.40  
  Purchase #5 $39.40   13.736%   $44.812   $44.81   $44.80   $44.80  
  Purchase #6 $40.77   7.478%   $43.8188   $43.82   $43.80   $43.80  
  Purchase #7 $187.46   11.491%   $209.001   $209.00   $209.00   $209.00  
  7 purchase totals = $905.78       $992.7862   $992.78   $992.75   $992.80