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 $239.83   11.506%   $267.4248   $267.42   $267.40   $267.40  
  Purchase #2 $179.70   8.541%   $195.0482   $195.05   $195.05   $195.00  
  Purchase #3 $210.73   12.161%   $236.3569   $236.36   $236.35   $236.40  
  Purchase #4 $32.80   4.339%   $34.2232   $34.22   $34.20   $34.20  
  Purchase #5 $187.97   3.379%   $194.3215   $194.32   $194.30   $194.30  
  Purchase #6 $166.61   4.308%   $173.7876   $173.79   $173.80   $173.80  
  Purchase #7 $239.76   9.435%   $262.3814   $262.38   $262.40   $262.40  
  7 purchase totals = $1,257.40       $1,363.5436   $1,363.54   $1,363.50   $1,363.50