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 $58.41   6.427%   $62.164   $62.16   $62.15   $62.20  
  Purchase #2 $179.32   13.277%   $203.1283   $203.13   $203.15   $203.10  
  Purchase #3 $16.51   10.401%   $18.2272   $18.23   $18.25   $18.20  
  Purchase #4 $57.95   11.143%   $64.4074   $64.41   $64.40   $64.40  
  Purchase #5 $76.43   10.823%   $84.702   $84.70   $84.70   $84.70  
  Purchase #6 $63.99   10.194%   $70.5131   $70.51   $70.50   $70.50  
  Purchase #7 $210.80   11.804%   $235.6828   $235.68   $235.70   $235.70  
  7 purchase totals = $663.41       $738.8248   $738.82   $738.85   $738.80