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 $182.42   11.558%   $203.5041   $203.50   $203.50   $203.50  
  Purchase #2 $250.47   13.722%   $284.8395   $284.84   $284.85   $284.80  
  Purchase #3 $32.83   7.497%   $35.2913   $35.29   $35.30   $35.30  
  Purchase #4 $196.79   12.696%   $221.7745   $221.77   $221.75   $221.80  
  Purchase #5 $123.81   10.843%   $137.2347   $137.23   $137.25   $137.20  
  Purchase #6 $19.87   9.862%   $21.8296   $21.83   $21.85   $21.80  
  Purchase #7 $234.49   11.610%   $261.7143   $261.71   $261.70   $261.70  
  7 purchase totals = $1,040.68       $1,166.1880   $1,166.17   $1,166.20   $1,166.10