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 $206.98   9.374%   $226.3823   $226.38   $226.40   $226.40  
  Purchase #2 $154.63   7.711%   $166.5535   $166.55   $166.55   $166.60  
  Purchase #3 $107.86   10.580%   $119.2716   $119.27   $119.25   $119.30  
  Purchase #4 $239.33   7.732%   $257.835   $257.84   $257.85   $257.80  
  Purchase #5 $224.38   3.862%   $233.0456   $233.05   $233.05   $233.00  
  Purchase #6 $200.30   5.573%   $211.4627   $211.46   $211.45   $211.50  
  Purchase #7 $69.34   4.682%   $72.5865   $72.59   $72.60   $72.60  
  7 purchase totals = $1,202.82       $1,287.1372   $1,287.14   $1,287.15   $1,287.20