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 $44.27   8.835%   $48.1813   $48.18   $48.20   $48.20  
  Purchase #2 $210.72   13.694%   $239.576   $239.58   $239.60   $239.60  
  Purchase #3 $60.29   12.837%   $68.0294   $68.03   $68.05   $68.00  
  Purchase #4 $127.26   3.548%   $131.7752   $131.78   $131.80   $131.80  
  Purchase #5 $27.62   8.494%   $29.966   $29.97   $29.95   $30.00  
  Purchase #6 $148.41   4.782%   $155.507   $155.51   $155.50   $155.50  
  Purchase #7 $236.42   10.255%   $260.6649   $260.66   $260.65   $260.70  
  7 purchase totals = $854.99       $933.6998   $933.71   $933.75   $933.80