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 $239.50   9.289%   $261.7472   $261.75   $261.75   $261.70  
  Purchase #2 $244.76   12.238%   $274.7137   $274.71   $274.70   $274.70  
  Purchase #3 $41.64   9.511%   $45.6004   $45.60   $45.60   $45.60  
  Purchase #4 $156.95   13.816%   $178.6342   $178.63   $178.65   $178.60  
  Purchase #5 $121.31   3.353%   $125.3775   $125.38   $125.40   $125.40  
  Purchase #6 $23.63   7.865%   $25.4885   $25.49   $25.50   $25.50  
  Purchase #7 $86.92   13.528%   $98.6785   $98.68   $98.70   $98.70  
  7 purchase totals = $914.71       $1,010.2400   $1,010.24   $1,010.30   $1,010.20