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 $104.67   13.637%   $118.9438   $118.94   $118.95   $118.90  
  Purchase #2 $249.35   5.294%   $262.5506   $262.55   $262.55   $262.60  
  Purchase #3 $42.87   3.105%   $44.2011   $44.20   $44.20   $44.20  
  Purchase #4 $60.60   6.414%   $64.4869   $64.49   $64.50   $64.50  
  Purchase #5 $217.49   13.212%   $246.2248   $246.22   $246.20   $246.20  
  Purchase #6 $6.89   6.535%   $7.3403   $7.34   $7.35   $7.30  
  Purchase #7 $247.69   6.389%   $263.5149   $263.51   $263.50   $263.50  
  7 purchase totals = $929.56       $1,007.2624   $1,007.25   $1,007.25   $1,007.20