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 $51.84   6.390%   $55.1526   $55.15   $55.15   $55.20  
  Purchase #2 $126.60   5.447%   $133.4959   $133.50   $133.50   $133.50  
  Purchase #3 $147.99   3.708%   $153.4775   $153.48   $153.50   $153.50  
  Purchase #4 $118.46   6.293%   $125.9147   $125.91   $125.90   $125.90  
  Purchase #5 $178.97   3.496%   $185.2268   $185.23   $185.25   $185.20  
  Purchase #6 $15.49   5.352%   $16.319   $16.32   $16.30   $16.30  
  Purchase #7 $245.89   5.486%   $259.3795   $259.38   $259.40   $259.40  
  7 purchase totals = $885.24       $928.9660   $928.97   $929.00   $929.00