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 $208.43   6.369%   $221.7049   $221.70   $221.70   $221.70  
  Purchase #2 $125.87   13.105%   $142.3653   $142.37   $142.35   $142.40  
  Purchase #3 $42.91   4.359%   $44.7804   $44.78   $44.80   $44.80  
  Purchase #4 $233.90   5.102%   $245.8336   $245.83   $245.85   $245.80  
  Purchase #5 $121.76   8.577%   $132.2034   $132.20   $132.20   $132.20  
  Purchase #6 $208.72   11.428%   $232.5725   $232.57   $232.55   $232.60  
  Purchase #7 $114.36   8.475%   $124.052   $124.05   $124.05   $124.10  
  7 purchase totals = $1,055.95       $1,143.5121   $1,143.50   $1,143.50   $1,143.60