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 $246.89   6.719%   $263.4785   $263.48   $263.50   $263.50  
  Purchase #2 $93.98   13.495%   $106.6626   $106.66   $106.65   $106.70  
  Purchase #3 $231.91   9.377%   $253.6562   $253.66   $253.65   $253.70  
  Purchase #4 $51.77   13.589%   $58.805   $58.81   $58.80   $58.80  
  Purchase #5 $206.73   7.353%   $221.9309   $221.93   $221.95   $221.90  
  Purchase #6 $136.36   3.558%   $141.2117   $141.21   $141.20   $141.20  
  Purchase #7 $250.61   11.815%   $280.2196   $280.22   $280.20   $280.20  
  7 purchase totals = $1,218.25       $1,325.9645   $1,325.97   $1,325.95   $1,326.00