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 $197.45   12.738%   $222.6012   $222.60   $222.60   $222.60  
  Purchase #2 $41.93   11.426%   $46.7209   $46.72   $46.70   $46.70  
  Purchase #3 $13.57   5.722%   $14.3465   $14.35   $14.35   $14.30  
  Purchase #4 $91.81   11.451%   $102.3232   $102.32   $102.30   $102.30  
  Purchase #5 $101.63   13.336%   $115.1834   $115.18   $115.20   $115.20  
  Purchase #6 $159.38   3.505%   $164.9663   $164.97   $164.95   $165.00  
  Purchase #7 $82.50   4.839%   $86.4922   $86.49   $86.50   $86.50  
  7 purchase totals = $688.27       $752.6337   $752.63   $752.60   $752.60