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 $148.44   13.419%   $168.3592   $168.36   $168.35   $168.40  
  Purchase #2 $54.74   11.329%   $60.9415   $60.94   $60.95   $60.90  
  Purchase #3 $93.73   4.399%   $97.8532   $97.85   $97.85   $97.90  
  Purchase #4 $121.84   8.387%   $132.0587   $132.06   $132.05   $132.10  
  Purchase #5 $218.42   12.104%   $244.8576   $244.86   $244.85   $244.90  
  Purchase #6 $81.77   12.201%   $91.7468   $91.75   $91.75   $91.70  
  Purchase #7 $152.39   4.624%   $159.4365   $159.44   $159.45   $159.40  
  7 purchase totals = $871.33       $955.2535   $955.26   $955.25   $955.30