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 $65.38   9.345%   $71.4898   $71.49   $71.50   $71.50  
  Purchase #2 $249.51   6.686%   $266.1922   $266.19   $266.20   $266.20  
  Purchase #3 $77.34   12.130%   $86.7213   $86.72   $86.70   $86.70  
  Purchase #4 $96.85   10.645%   $107.1597   $107.16   $107.15   $107.20  
  Purchase #5 $230.90   8.355%   $250.1917   $250.19   $250.20   $250.20  
  Purchase #6 $27.36   5.625%   $28.899   $28.90   $28.90   $28.90  
  Purchase #7 $218.98   8.353%   $237.2714   $237.27   $237.25   $237.30  
  7 purchase totals = $966.32       $1,047.9251   $1,047.92   $1,047.90   $1,048.00