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 $239.26   9.187%   $261.2408   $261.24   $261.25   $261.20  
  Purchase #2 $102.36   4.718%   $107.1893   $107.19   $107.20   $107.20  
  Purchase #3 $102.97   9.214%   $112.4577   $112.46   $112.45   $112.50  
  Purchase #4 $107.28   5.157%   $112.8124   $112.81   $112.80   $112.80  
  Purchase #5 $25.47   5.713%   $26.9251   $26.93   $26.95   $26.90  
  Purchase #6 $160.60   9.259%   $175.47   $175.47   $175.45   $175.50  
  Purchase #7 $111.66   6.610%   $119.0407   $119.04   $119.05   $119.00  
  7 purchase totals = $849.60       $915.1360   $915.14   $915.15   $915.10