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 $217.69   11.187%   $242.043   $242.04   $242.05   $242.00  
  Purchase #2 $72.28   4.723%   $75.6938   $75.69   $75.70   $75.70  
  Purchase #3 $250.76   12.356%   $281.7439   $281.74   $281.75   $281.70  
  Purchase #4 $96.27   12.138%   $107.9553   $107.96   $107.95   $108.00  
  Purchase #5 $188.42   13.643%   $214.1261   $214.13   $214.15   $214.10  
  Purchase #6 $132.32   9.583%   $145.0002   $145.00   $145.00   $145.00  
  Purchase #7 $123.55   13.532%   $140.2688   $140.27   $140.25   $140.30  
  7 purchase totals = $1,081.29       $1,206.8311   $1,206.83   $1,206.85   $1,206.80