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 $201.32   11.266%   $224.0007   $224.00   $224.00   $224.00  
  Purchase #2 $122.34   11.856%   $136.8446   $136.84   $136.85   $136.80  
  Purchase #3 $37.63   6.493%   $40.0733   $40.07   $40.05   $40.10  
  Purchase #4 $250.49   12.126%   $280.8644   $280.86   $280.85   $280.90  
  Purchase #5 $48.28   7.723%   $52.0087   $52.01   $52.00   $52.00  
  Purchase #6 $61.78   9.370%   $67.5688   $67.57   $67.55   $67.60  
  Purchase #7 $195.27   11.397%   $217.5249   $217.52   $217.50   $217.50  
  7 purchase totals = $917.11       $1,018.8854   $1,018.87   $1,018.80   $1,018.90