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 $231.62   6.382%   $246.402   $246.40   $246.40   $246.40  
  Purchase #2 $14.86   4.387%   $15.5119   $15.51   $15.50   $15.50  
  Purchase #3 $45.59   9.567%   $49.9516   $49.95   $49.95   $50.00  
  Purchase #4 $188.85   13.530%   $214.4014   $214.40   $214.40   $214.40  
  Purchase #5 $141.91   3.452%   $146.8087   $146.81   $146.80   $146.80  
  Purchase #6 $182.70   7.208%   $195.869   $195.87   $195.85   $195.90  
  Purchase #7 $177.61   3.231%   $183.3486   $183.35   $183.35   $183.30  
  7 purchase totals = $983.14       $1,052.2932   $1,052.29   $1,052.25   $1,052.30