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 $222.62   10.589%   $246.1932   $246.19   $246.20   $246.20  
  Purchase #2 $47.96   3.322%   $49.5532   $49.55   $49.55   $49.60  
  Purchase #3 $38.44   10.561%   $42.4996   $42.50   $42.50   $42.50  
  Purchase #4 $177.48   10.377%   $195.8971   $195.90   $195.90   $195.90  
  Purchase #5 $246.68   12.723%   $278.0651   $278.07   $278.05   $278.10  
  Purchase #6 $98.75   6.805%   $105.4699   $105.47   $105.45   $105.50  
  Purchase #7 $70.99   6.863%   $75.862   $75.86   $75.85   $75.90  
  7 purchase totals = $902.92       $993.5401   $993.54   $993.50   $993.70