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 $232.75   5.856%   $246.3798   $246.38   $246.40   $246.40  
  Purchase #2 $124.42   10.844%   $137.9121   $137.91   $137.90   $137.90  
  Purchase #3 $178.63   9.306%   $195.2533   $195.25   $195.25   $195.30  
  Purchase #4 $246.29   5.685%   $260.2916   $260.29   $260.30   $260.30  
  Purchase #5 $86.84   12.282%   $97.5057   $97.51   $97.50   $97.50  
  Purchase #6 $119.55   6.258%   $127.0314   $127.03   $127.05   $127.00  
  Purchase #7 $232.30   12.247%   $260.7498   $260.75   $260.75   $260.70  
  7 purchase totals = $1,220.78       $1,325.1237   $1,325.12   $1,325.15   $1,325.10