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 $208.95   3.872%   $217.0405   $217.04   $217.05   $217.00  
  Purchase #2 $149.44   5.485%   $157.6368   $157.64   $157.65   $157.60  
  Purchase #3 $87.25   3.476%   $90.2828   $90.28   $90.30   $90.30  
  Purchase #4 $216.99   4.258%   $226.2294   $226.23   $226.25   $226.20  
  Purchase #5 $195.38   9.372%   $213.691   $213.69   $213.70   $213.70  
  Purchase #6 $198.56   11.710%   $221.8114   $221.81   $221.80   $221.80  
  Purchase #7 $223.68   10.429%   $247.0076   $247.01   $247.00   $247.00  
  7 purchase totals = $1,280.25       $1,373.6995   $1,373.70   $1,373.75   $1,373.60