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 $14.37   13.219%   $16.2696   $16.27   $16.25   $16.30  
  Purchase #2 $227.62   5.816%   $240.8584   $240.86   $240.85   $240.90  
  Purchase #3 $15.86   5.458%   $16.7256   $16.73   $16.75   $16.70  
  Purchase #4 $206.79   5.863%   $218.9141   $218.91   $218.90   $218.90  
  Purchase #5 $33.82   7.388%   $36.3186   $36.32   $36.30   $36.30  
  Purchase #6 $137.87   7.465%   $148.162   $148.16   $148.15   $148.20  
  Purchase #7 $224.33   11.362%   $249.8184   $249.82   $249.80   $249.80  
  7 purchase totals = $860.66       $927.0667   $927.07   $927.00   $927.10