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 $84.66   11.591%   $94.4729   $94.47   $94.45   $94.50  
  Purchase #2 $60.86   9.131%   $66.4171   $66.42   $66.40   $66.40  
  Purchase #3 $139.49   9.702%   $153.0233   $153.02   $153.00   $153.00  
  Purchase #4 $55.51   12.424%   $62.4066   $62.41   $62.40   $62.40  
  Purchase #5 $191.62   11.544%   $213.7406   $213.74   $213.75   $213.70  
  Purchase #6 $81.34   9.322%   $88.9225   $88.92   $88.90   $88.90  
  Purchase #7 $211.66   5.273%   $222.8208   $222.82   $222.80   $222.80  
  7 purchase totals = $825.14       $901.8038   $901.80   $901.70   $901.70