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 $233.80   11.598%   $260.9161   $260.92   $260.90   $260.90  
  Purchase #2 $109.63   9.136%   $119.6458   $119.65   $119.65   $119.60  
  Purchase #3 $56.38   11.292%   $62.7464   $62.75   $62.75   $62.70  
  Purchase #4 $178.42   9.128%   $194.7062   $194.71   $194.70   $194.70  
  Purchase #5 $30.58   7.221%   $32.7882   $32.79   $32.80   $32.80  
  Purchase #6 $227.64   4.330%   $237.4968   $237.50   $237.50   $237.50  
  Purchase #7 $87.92   8.750%   $95.613   $95.61   $95.60   $95.60  
  7 purchase totals = $924.37       $1,003.9125   $1,003.93   $1,003.90   $1,003.80