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 $43.97   6.369%   $46.7704   $46.77   $46.75   $46.80  
  Purchase #2 $227.25   8.772%   $247.1844   $247.18   $247.20   $247.20  
  Purchase #3 $116.89   4.466%   $122.1103   $122.11   $122.10   $122.10  
  Purchase #4 $54.34   11.238%   $60.4467   $60.45   $60.45   $60.40  
  Purchase #5 $206.96   5.129%   $217.575   $217.58   $217.60   $217.60  
  Purchase #6 $213.68   10.102%   $235.266   $235.27   $235.25   $235.30  
  Purchase #7 $51.57   12.712%   $58.1256   $58.13   $58.15   $58.10  
  7 purchase totals = $914.66       $987.4784   $987.49   $987.50   $987.50