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 $208.40   8.758%   $226.6517   $226.65   $226.65   $226.70  
  Purchase #2 $8.97   4.856%   $9.4056   $9.41   $9.40   $9.40  
  Purchase #3 $96.26   4.607%   $100.6947   $100.69   $100.70   $100.70  
  Purchase #4 $233.43   12.593%   $262.8258   $262.83   $262.85   $262.80  
  Purchase #5 $116.46   13.804%   $132.5361   $132.54   $132.55   $132.50  
  Purchase #6 $212.76   9.276%   $232.4956   $232.50   $232.50   $232.50  
  Purchase #7 $30.48   5.377%   $32.1189   $32.12   $32.10   $32.10  
  7 purchase totals = $906.76       $996.7284   $996.74   $996.75   $996.70