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 $245.76   6.692%   $262.2063   $262.21   $262.20   $262.20  
  Purchase #2 $41.75   13.562%   $47.4121   $47.41   $47.40   $47.40  
  Purchase #3 $15.34   9.527%   $16.8014   $16.80   $16.80   $16.80  
  Purchase #4 $115.36   3.662%   $119.5845   $119.58   $119.60   $119.60  
  Purchase #5 $106.49   9.207%   $116.2945   $116.29   $116.30   $116.30  
  Purchase #6 $21.62   10.805%   $23.956   $23.96   $23.95   $24.00  
  Purchase #7 $9.47   13.530%   $10.7513   $10.75   $10.75   $10.80  
  7 purchase totals = $555.79       $597.0061   $597.00   $597.00   $597.10