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 $53.95   11.764%   $60.2967   $60.30   $60.30   $60.30  
  Purchase #2 $123.41   6.772%   $131.7673   $131.77   $131.75   $131.80  
  Purchase #3 $116.92   8.549%   $126.9155   $126.92   $126.90   $126.90  
  Purchase #4 $142.67   11.134%   $158.5549   $158.55   $158.55   $158.60  
  Purchase #5 $55.68   12.475%   $62.6261   $62.63   $62.65   $62.60  
  Purchase #6 $108.64   3.310%   $112.236   $112.24   $112.25   $112.20  
  Purchase #7 $120.86   13.302%   $136.9368   $136.94   $136.95   $136.90  
  7 purchase totals = $722.13       $789.3333   $789.35   $789.35   $789.30