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 $244.85   8.722%   $266.2058   $266.21   $266.20   $266.20  
  Purchase #2 $189.36   11.230%   $210.6251   $210.63   $210.65   $210.60  
  Purchase #3 $48.42   4.300%   $50.5021   $50.50   $50.50   $50.50  
  Purchase #4 $12.96   13.796%   $14.748   $14.75   $14.75   $14.70  
  Purchase #5 $78.56   13.378%   $89.0698   $89.07   $89.05   $89.10  
  Purchase #6 $41.52   6.371%   $44.1652   $44.17   $44.15   $44.20  
  Purchase #7 $247.28   11.218%   $275.0199   $275.02   $275.00   $275.00  
  7 purchase totals = $862.95       $950.3359   $950.35   $950.30   $950.30