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 $242.75   5.462%   $256.009   $256.01   $256.00   $256.00  
  Purchase #2 $224.30   8.196%   $242.6836   $242.68   $242.70   $242.70  
  Purchase #3 $149.29   6.178%   $158.5131   $158.51   $158.50   $158.50  
  Purchase #4 $57.67   5.301%   $60.7271   $60.73   $60.75   $60.70  
  Purchase #5 $225.79   10.434%   $249.3489   $249.35   $249.35   $249.30  
  Purchase #6 $231.48   12.573%   $260.584   $260.58   $260.60   $260.60  
  Purchase #7 $222.49   6.533%   $237.0253   $237.03   $237.05   $237.00  
  7 purchase totals = $1,353.77       $1,464.8910   $1,464.89   $1,464.95   $1,464.80