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 $119.68   13.836%   $136.2389   $136.24   $136.25   $136.20  
  Purchase #2 $233.45   5.347%   $245.9326   $245.93   $245.95   $245.90  
  Purchase #3 $148.90   5.638%   $157.295   $157.30   $157.30   $157.30  
  Purchase #4 $162.67   4.799%   $170.4765   $170.48   $170.50   $170.50  
  Purchase #5 $197.85   5.112%   $207.9641   $207.96   $207.95   $208.00  
  Purchase #6 $58.30   9.322%   $63.7347   $63.73   $63.75   $63.70  
  Purchase #7 $132.76   8.652%   $144.2464   $144.25   $144.25   $144.20  
  7 purchase totals = $1,053.61       $1,125.8882   $1,125.89   $1,125.95   $1,125.80