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 $42.51   5.612%   $44.8957   $44.90   $44.90   $44.90  
  Purchase #2 $54.86   8.467%   $59.505   $59.51   $59.50   $59.50  
  Purchase #3 $100.38   11.611%   $112.0351   $112.04   $112.05   $112.00  
  Purchase #4 $60.83   5.574%   $64.2207   $64.22   $64.20   $64.20  
  Purchase #5 $135.36   8.128%   $146.3621   $146.36   $146.35   $146.40  
  Purchase #6 $245.62   8.391%   $266.23   $266.23   $266.25   $266.20  
  Purchase #7 $171.25   5.399%   $180.4958   $180.50   $180.50   $180.50  
  7 purchase totals = $810.81       $873.7444   $873.76   $873.75   $873.70