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 $62.27   11.636%   $69.5157   $69.52   $69.50   $69.50  
  Purchase #2 $202.37   11.763%   $226.1748   $226.17   $226.15   $226.20  
  Purchase #3 $161.39   5.343%   $170.0131   $170.01   $170.00   $170.00  
  Purchase #4 $36.26   6.175%   $38.4991   $38.50   $38.50   $38.50  
  Purchase #5 $68.80   12.248%   $77.2266   $77.23   $77.25   $77.20  
  Purchase #6 $20.47   4.372%   $21.3649   $21.36   $21.35   $21.40  
  Purchase #7 $224.38   5.588%   $236.9184   $236.92   $236.90   $236.90  
  7 purchase totals = $775.94       $839.7126   $839.71   $839.65   $839.70