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 $16.33   3.397%   $16.8847   $16.88   $16.90   $16.90  
  Purchase #2 $234.46   8.252%   $253.8076   $253.81   $253.80   $253.80  
  Purchase #3 $18.48   4.414%   $19.2957   $19.30   $19.30   $19.30  
  Purchase #4 $203.70   6.777%   $217.5047   $217.50   $217.50   $217.50  
  Purchase #5 $11.95   6.765%   $12.7584   $12.76   $12.75   $12.80  
  Purchase #6 $120.28   4.448%   $125.6301   $125.63   $125.65   $125.60  
  Purchase #7 $225.88   11.616%   $252.1182   $252.12   $252.10   $252.10  
  7 purchase totals = $831.08       $897.9994   $898.00   $898.00   $898.00