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 $56.60   7.403%   $60.7901   $60.79   $60.80   $60.80  
  Purchase #2 $216.58   12.804%   $244.3109   $244.31   $244.30   $244.30  
  Purchase #3 $26.72   4.368%   $27.8871   $27.89   $27.90   $27.90  
  Purchase #4 $157.63   6.677%   $168.155   $168.16   $168.15   $168.20  
  Purchase #5 $208.94   12.383%   $234.813   $234.81   $234.80   $234.80  
  Purchase #6 $10.73   5.141%   $11.2816   $11.28   $11.30   $11.30  
  Purchase #7 $62.26   9.544%   $68.2021   $68.20   $68.20   $68.20  
  7 purchase totals = $739.46       $815.4398   $815.44   $815.45   $815.50