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 $208.76   6.332%   $221.9787   $221.98   $222.00   $222.00  
  Purchase #2 $222.44   13.237%   $251.8844   $251.88   $251.90   $251.90  
  Purchase #3 $142.63   8.576%   $154.8619   $154.86   $154.85   $154.90  
  Purchase #4 $6.88   12.284%   $7.7251   $7.73   $7.75   $7.70  
  Purchase #5 $86.62   5.252%   $91.1693   $91.17   $91.15   $91.20  
  Purchase #6 $51.87   6.209%   $55.0906   $55.09   $55.10   $55.10  
  Purchase #7 $246.50   12.175%   $276.5114   $276.51   $276.50   $276.50  
  7 purchase totals = $965.70       $1,059.2214   $1,059.22   $1,059.25   $1,059.30