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 $60.40   11.761%   $67.5036   $67.50   $67.50   $67.50  
  Purchase #2 $92.63   4.109%   $96.4362   $96.44   $96.45   $96.40  
  Purchase #3 $81.85   6.113%   $86.8535   $86.85   $86.85   $86.90  
  Purchase #4 $46.65   11.287%   $51.9154   $51.92   $51.90   $51.90  
  Purchase #5 $186.36   11.498%   $207.7877   $207.79   $207.80   $207.80  
  Purchase #6 $208.56   3.294%   $215.43   $215.43   $215.45   $215.40  
  Purchase #7 $121.36   13.227%   $137.4123   $137.41   $137.40   $137.40  
  7 purchase totals = $797.81       $863.3387   $863.34   $863.35   $863.30