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 $234.38   13.499%   $266.019   $266.02   $266.00   $266.00  
  Purchase #2 $214.90   11.734%   $240.1164   $240.12   $240.10   $240.10  
  Purchase #3 $94.43   6.334%   $100.4112   $100.41   $100.40   $100.40  
  Purchase #4 $197.98   9.862%   $217.5048   $217.50   $217.50   $217.50  
  Purchase #5 $208.58   3.110%   $215.0668   $215.07   $215.05   $215.10  
  Purchase #6 $65.30   12.664%   $73.5696   $73.57   $73.55   $73.60  
  Purchase #7 $146.46   7.607%   $157.6012   $157.60   $157.60   $157.60  
  7 purchase totals = $1,162.03       $1,270.2890   $1,270.29   $1,270.20   $1,270.30