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 $56.73   12.518%   $63.8315   $63.83   $63.85   $63.80  
  Purchase #2 $249.41   10.307%   $275.1167   $275.12   $275.10   $275.10  
  Purchase #3 $190.47   8.267%   $206.2162   $206.22   $206.20   $206.20  
  Purchase #4 $109.39   5.570%   $115.483   $115.48   $115.50   $115.50  
  Purchase #5 $199.42   3.436%   $206.2721   $206.27   $206.25   $206.30  
  Purchase #6 $214.82   6.313%   $228.3816   $228.38   $228.40   $228.40  
  Purchase #7 $131.98   4.350%   $137.7211   $137.72   $137.70   $137.70  
  7 purchase totals = $1,152.22       $1,233.0222   $1,233.02   $1,233.00   $1,233.00