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 $210.49   12.491%   $236.7823   $236.78   $236.80   $236.80  
  Purchase #2 $19.93   10.105%   $21.9439   $21.94   $21.95   $21.90  
  Purchase #3 $126.57   4.817%   $132.6669   $132.67   $132.65   $132.70  
  Purchase #4 $153.67   8.834%   $167.2452   $167.25   $167.25   $167.20  
  Purchase #5 $29.89   5.289%   $31.4709   $31.47   $31.45   $31.50  
  Purchase #6 $139.36   6.325%   $148.1745   $148.17   $148.15   $148.20  
  Purchase #7 $244.95   11.255%   $272.5191   $272.52   $272.50   $272.50  
  7 purchase totals = $924.86       $1,010.8028   $1,010.80   $1,010.75   $1,010.80