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 $160.72   9.201%   $175.5078   $175.51   $175.50   $175.50  
  Purchase #2 $244.74   7.314%   $262.6403   $262.64   $262.65   $262.60  
  Purchase #3 $140.48   4.373%   $146.6232   $146.62   $146.60   $146.60  
  Purchase #4 $247.69   8.782%   $269.4421   $269.44   $269.45   $269.40  
  Purchase #5 $183.45   4.244%   $191.2356   $191.24   $191.25   $191.20  
  Purchase #6 $65.70   5.690%   $69.4383   $69.44   $69.45   $69.40  
  Purchase #7 $93.49   12.579%   $105.2501   $105.25   $105.25   $105.30  
  7 purchase totals = $1,136.27       $1,220.1374   $1,220.14   $1,220.15   $1,220.00