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 $222.82   10.754%   $246.7821   $246.78   $246.80   $246.80  
  Purchase #2 $188.34   12.752%   $212.3571   $212.36   $212.35   $212.40  
  Purchase #3 $148.89   6.625%   $158.754   $158.75   $158.75   $158.80  
  Purchase #4 $222.54   4.534%   $232.63   $232.63   $232.65   $232.60  
  Purchase #5 $84.26   10.149%   $92.8115   $92.81   $92.80   $92.80  
  Purchase #6 $213.96   5.153%   $224.9854   $224.99   $225.00   $225.00  
  Purchase #7 $170.67   13.854%   $194.3146   $194.31   $194.30   $194.30  
  7 purchase totals = $1,251.48       $1,362.6347   $1,362.63   $1,362.65   $1,362.70