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 $216.37   9.227%   $236.3345   $236.33   $236.35   $236.30  
  Purchase #2 $224.88   12.756%   $253.5657   $253.57   $253.55   $253.60  
  Purchase #3 $240.44   3.778%   $249.5238   $249.52   $249.50   $249.50  
  Purchase #4 $117.89   5.362%   $124.2113   $124.21   $124.20   $124.20  
  Purchase #5 $11.69   11.409%   $13.0237   $13.02   $13.00   $13.00  
  Purchase #6 $217.61   4.703%   $227.8442   $227.84   $227.85   $227.80  
  Purchase #7 $233.52   4.602%   $244.2666   $244.27   $244.25   $244.30  
  7 purchase totals = $1,262.40       $1,348.7698   $1,348.76   $1,348.70   $1,348.70