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 $66.97   4.824%   $70.2006   $70.20   $70.20   $70.20  
  Purchase #2 $157.97   12.822%   $178.2249   $178.22   $178.20   $178.20  
  Purchase #3 $92.64   13.203%   $104.8713   $104.87   $104.85   $104.90  
  Purchase #4 $146.97   9.794%   $161.3642   $161.36   $161.35   $161.40  
  Purchase #5 $190.26   4.408%   $198.6467   $198.65   $198.65   $198.60  
  Purchase #6 $22.50   7.247%   $24.1306   $24.13   $24.15   $24.10  
  Purchase #7 $199.83   12.209%   $224.2272   $224.23   $224.25   $224.20  
  7 purchase totals = $877.14       $961.6655   $961.66   $961.65   $961.60