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 $227.93   7.477%   $244.9723   $244.97   $244.95   $245.00  
  Purchase #2 $233.30   12.247%   $261.8723   $261.87   $261.85   $261.90  
  Purchase #3 $170.67   12.406%   $191.8433   $191.84   $191.85   $191.80  
  Purchase #4 $61.38   8.650%   $66.6894   $66.69   $66.70   $66.70  
  Purchase #5 $118.30   7.298%   $126.9335   $126.93   $126.95   $126.90  
  Purchase #6 $188.35   4.283%   $196.417   $196.42   $196.40   $196.40  
  Purchase #7 $141.71   7.422%   $152.2277   $152.23   $152.25   $152.20  
  7 purchase totals = $1,141.64       $1,240.9555   $1,240.95   $1,240.95   $1,240.90