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 $200.68   6.648%   $214.0212   $214.02   $214.00   $214.00  
  Purchase #2 $104.38   10.348%   $115.1812   $115.18   $115.20   $115.20  
  Purchase #3 $182.28   13.357%   $206.6271   $206.63   $206.65   $206.60  
  Purchase #4 $215.49   8.565%   $233.9467   $233.95   $233.95   $233.90  
  Purchase #5 $155.83   3.228%   $160.8602   $160.86   $160.85   $160.90  
  Purchase #6 $237.25   3.477%   $245.4992   $245.50   $245.50   $245.50  
  Purchase #7 $178.29   13.652%   $202.6302   $202.63   $202.65   $202.60  
  7 purchase totals = $1,274.20       $1,378.7658   $1,378.77   $1,378.80   $1,378.70