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 $244.69   8.842%   $266.3255   $266.33   $266.35   $266.30  
  Purchase #2 $62.90   12.433%   $70.7204   $70.72   $70.70   $70.70  
  Purchase #3 $69.54   7.401%   $74.6867   $74.69   $74.70   $74.70  
  Purchase #4 $19.48   6.532%   $20.7524   $20.75   $20.75   $20.80  
  Purchase #5 $110.66   13.259%   $125.3324   $125.33   $125.35   $125.30  
  Purchase #6 $167.43   12.726%   $188.7371   $188.74   $188.75   $188.70  
  Purchase #7 $189.97   12.243%   $213.228   $213.23   $213.25   $213.20  
  7 purchase totals = $864.67       $959.7825   $959.79   $959.85   $959.70