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 $225.77   12.337%   $253.6232   $253.62   $253.60   $253.60  
  Purchase #2 $119.65   10.680%   $132.4286   $132.43   $132.45   $132.40  
  Purchase #3 $55.54   9.339%   $60.7269   $60.73   $60.75   $60.70  
  Purchase #4 $157.73   13.187%   $178.5299   $178.53   $178.55   $178.50  
  Purchase #5 $119.89   9.852%   $131.7016   $131.70   $131.70   $131.70  
  Purchase #6 $233.51   5.534%   $246.4324   $246.43   $246.45   $246.40  
  Purchase #7 $26.84   10.397%   $29.6306   $29.63   $29.65   $29.60  
  7 purchase totals = $938.93       $1,033.0732   $1,033.07   $1,033.15   $1,032.90