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 $199.26   8.861%   $216.9164   $216.92   $216.90   $216.90  
  Purchase #2 $119.96   3.839%   $124.5653   $124.57   $124.55   $124.60  
  Purchase #3 $109.54   7.566%   $117.8278   $117.83   $117.85   $117.80  
  Purchase #4 $177.85   13.758%   $202.3186   $202.32   $202.30   $202.30  
  Purchase #5 $205.61   13.651%   $233.6778   $233.68   $233.70   $233.70  
  Purchase #6 $189.30   13.269%   $214.4182   $214.42   $214.40   $214.40  
  Purchase #7 $215.88   8.626%   $234.5018   $234.50   $234.50   $234.50  
  7 purchase totals = $1,217.40       $1,344.2259   $1,344.24   $1,344.20   $1,344.20