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 $209.78   8.507%   $227.626   $227.63   $227.65   $227.60  
  Purchase #2 $93.35   9.133%   $101.8757   $101.88   $101.90   $101.90  
  Purchase #3 $134.43   13.463%   $152.5283   $152.53   $152.55   $152.50  
  Purchase #4 $175.83   8.337%   $190.4889   $190.49   $190.50   $190.50  
  Purchase #5 $223.77   5.620%   $236.3459   $236.35   $236.35   $236.30  
  Purchase #6 $226.44   3.294%   $233.8989   $233.90   $233.90   $233.90  
  Purchase #7 $215.65   10.186%   $237.6161   $237.62   $237.60   $237.60  
  7 purchase totals = $1,279.25       $1,380.3798   $1,380.40   $1,380.45   $1,380.30