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 $182.66   8.119%   $197.4902   $197.49   $197.50   $197.50  
  Purchase #2 $10.85   6.847%   $11.5929   $11.59   $11.60   $11.60  
  Purchase #3 $21.54   8.628%   $23.3985   $23.40   $23.40   $23.40  
  Purchase #4 $48.47   5.630%   $51.1989   $51.20   $51.20   $51.20  
  Purchase #5 $90.31   3.771%   $93.7156   $93.72   $93.70   $93.70  
  Purchase #6 $125.51   3.123%   $129.4297   $129.43   $129.45   $129.40  
  Purchase #7 $223.72   6.563%   $238.4027   $238.40   $238.40   $238.40  
  7 purchase totals = $703.06       $745.2285   $745.23   $745.25   $745.20