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 $83.94   12.179%   $94.1631   $94.16   $94.15   $94.20  
  Purchase #2 $57.61   8.129%   $62.2931   $62.29   $62.30   $62.30  
  Purchase #3 $173.39   6.531%   $184.7141   $184.71   $184.70   $184.70  
  Purchase #4 $217.33   11.521%   $242.3686   $242.37   $242.35   $242.40  
  Purchase #5 $49.48   4.427%   $51.6705   $51.67   $51.65   $51.70  
  Purchase #6 $66.86   4.164%   $69.6441   $69.64   $69.65   $69.60  
  Purchase #7 $214.82   13.543%   $243.9131   $243.91   $243.90   $243.90  
  7 purchase totals = $863.43       $948.7666   $948.75   $948.70   $948.80