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 $65.87   10.298%   $72.6533   $72.65   $72.65   $72.70  
  Purchase #2 $224.77   8.774%   $244.4913   $244.49   $244.50   $244.50  
  Purchase #3 $54.41   8.389%   $58.9745   $58.97   $58.95   $59.00  
  Purchase #4 $195.64   13.555%   $222.159   $222.16   $222.15   $222.20  
  Purchase #5 $178.26   11.579%   $198.9007   $198.90   $198.90   $198.90  
  Purchase #6 $130.62   8.328%   $141.498   $141.50   $141.50   $141.50  
  Purchase #7 $215.95   11.283%   $240.3156   $240.32   $240.30   $240.30  
  7 purchase totals = $1,065.52       $1,178.9924   $1,178.99   $1,178.95   $1,179.10