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 $125.38   5.568%   $132.3612   $132.36   $132.35   $132.40  
  Purchase #2 $53.77   4.355%   $56.1117   $56.11   $56.10   $56.10  
  Purchase #3 $19.96   13.163%   $22.5873   $22.59   $22.60   $22.60  
  Purchase #4 $228.55   12.553%   $257.2399   $257.24   $257.25   $257.20  
  Purchase #5 $153.68   5.522%   $162.1662   $162.17   $162.15   $162.20  
  Purchase #6 $84.43   8.511%   $91.6158   $91.62   $91.60   $91.60  
  Purchase #7 $14.36   10.749%   $15.9036   $15.90   $15.90   $15.90  
  7 purchase totals = $680.13       $737.9857   $737.99   $737.95   $738.00