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 $192.71   5.825%   $203.9354   $203.94   $203.95   $203.90  
  Purchase #2 $125.96   4.381%   $131.4783   $131.48   $131.50   $131.50  
  Purchase #3 $227.63   6.313%   $242.0003   $242.00   $242.00   $242.00  
  Purchase #4 $32.91   7.563%   $35.399   $35.40   $35.40   $35.40  
  Purchase #5 $6.44   3.348%   $6.6556   $6.66   $6.65   $6.70  
  Purchase #6 $119.70   11.369%   $133.3087   $133.31   $133.30   $133.30  
  Purchase #7 $46.86   3.208%   $48.3633   $48.36   $48.35   $48.40  
  7 purchase totals = $752.21       $801.1406   $801.15   $801.15   $801.20