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 $248.54   11.788%   $277.8379   $277.84   $277.85   $277.80  
  Purchase #2 $245.72   6.762%   $262.3356   $262.34   $262.35   $262.30  
  Purchase #3 $229.59   11.737%   $256.537   $256.54   $256.55   $256.50  
  Purchase #4 $52.76   3.354%   $54.5296   $54.53   $54.55   $54.50  
  Purchase #5 $208.41   8.794%   $226.7376   $226.74   $226.75   $226.70  
  Purchase #6 $48.44   3.549%   $50.1591   $50.16   $50.15   $50.20  
  Purchase #7 $173.33   6.716%   $184.9708   $184.97   $184.95   $185.00  
  7 purchase totals = $1,206.79       $1,313.1076   $1,313.12   $1,313.15   $1,313.00