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 $209.78   11.164%   $233.1998   $233.20   $233.20   $233.20  
  Purchase #2 $70.25   13.434%   $79.6874   $79.69   $79.70   $79.70  
  Purchase #3 $54.31   7.668%   $58.4745   $58.47   $58.45   $58.50  
  Purchase #4 $203.83   5.603%   $215.2506   $215.25   $215.25   $215.30  
  Purchase #5 $232.95   5.105%   $244.8421   $244.84   $244.85   $244.80  
  Purchase #6 $14.25   9.787%   $15.6446   $15.64   $15.65   $15.60  
  Purchase #7 $81.92   4.752%   $85.8128   $85.81   $85.80   $85.80  
  7 purchase totals = $867.29       $932.9118   $932.90   $932.90   $932.90