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 $244.81   5.853%   $259.1387   $259.14   $259.15   $259.10  
  Purchase #2 $151.63   4.665%   $158.7035   $158.70   $158.70   $158.70  
  Purchase #3 $207.43   5.822%   $219.5066   $219.51   $219.50   $219.50  
  Purchase #4 $91.53   7.647%   $98.5293   $98.53   $98.55   $98.50  
  Purchase #5 $180.44   10.671%   $199.6948   $199.69   $199.70   $199.70  
  Purchase #6 $163.31   11.125%   $181.4782   $181.48   $181.50   $181.50  
  Purchase #7 $18.55   4.486%   $19.3822   $19.38   $19.40   $19.40  
  7 purchase totals = $1,057.70       $1,136.4333   $1,136.43   $1,136.50   $1,136.40