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 $243.95   6.266%   $259.2359   $259.24   $259.25   $259.20  
  Purchase #2 $13.89   4.318%   $14.4898   $14.49   $14.50   $14.50  
  Purchase #3 $182.66   4.290%   $190.4961   $190.50   $190.50   $190.50  
  Purchase #4 $114.62   9.787%   $125.8379   $125.84   $125.85   $125.80  
  Purchase #5 $206.60   4.654%   $216.2152   $216.22   $216.20   $216.20  
  Purchase #6 $57.63   6.446%   $61.3448   $61.34   $61.35   $61.30  
  Purchase #7 $158.80   6.234%   $168.6996   $168.70   $168.70   $168.70  
  7 purchase totals = $978.15       $1,036.3193   $1,036.33   $1,036.35   $1,036.20