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 $238.44   10.123%   $262.5773   $262.58   $262.60   $262.60  
  Purchase #2 $115.79   8.268%   $125.3635   $125.36   $125.35   $125.40  
  Purchase #3 $60.38   6.337%   $64.2063   $64.21   $64.20   $64.20  
  Purchase #4 $245.84   3.669%   $254.8599   $254.86   $254.85   $254.90  
  Purchase #5 $200.66   4.858%   $210.4081   $210.41   $210.40   $210.40  
  Purchase #6 $185.82   10.406%   $205.1564   $205.16   $205.15   $205.20  
  Purchase #7 $33.34   3.792%   $34.6043   $34.60   $34.60   $34.60  
  7 purchase totals = $1,080.27       $1,157.1758   $1,157.18   $1,157.15   $1,157.30