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 $58.28   8.427%   $63.1913   $63.19   $63.20   $63.20  
  Purchase #2 $98.71   13.753%   $112.2856   $112.29   $112.30   $112.30  
  Purchase #3 $176.27   13.808%   $200.6094   $200.61   $200.60   $200.60  
  Purchase #4 $198.73   8.145%   $214.9166   $214.92   $214.90   $214.90  
  Purchase #5 $129.46   11.567%   $144.4346   $144.43   $144.45   $144.40  
  Purchase #6 $15.86   4.748%   $16.613   $16.61   $16.60   $16.60  
  Purchase #7 $192.64   11.745%   $215.2656   $215.27   $215.25   $215.30  
  7 purchase totals = $869.95       $967.3161   $967.32   $967.30   $967.30