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 $68.57   10.621%   $75.8528   $75.85   $75.85   $75.90  
  Purchase #2 $197.45   8.225%   $213.6903   $213.69   $213.70   $213.70  
  Purchase #3 $154.27   4.858%   $161.7644   $161.76   $161.75   $161.80  
  Purchase #4 $231.34   12.843%   $261.051   $261.05   $261.05   $261.10  
  Purchase #5 $12.50   5.867%   $13.2334   $13.23   $13.25   $13.20  
  Purchase #6 $57.38   9.487%   $62.8236   $62.82   $62.80   $62.80  
  Purchase #7 $220.42   10.417%   $243.3812   $243.38   $243.40   $243.40  
  7 purchase totals = $941.93       $1,031.7967   $1,031.78   $1,031.80   $1,031.90