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 $72.91   4.848%   $76.4447   $76.44   $76.45   $76.40  
  Purchase #2 $139.80   3.206%   $144.282   $144.28   $144.30   $144.30  
  Purchase #3 $152.31   4.186%   $158.6857   $158.69   $158.70   $158.70  
  Purchase #4 $60.84   11.677%   $67.9443   $67.94   $67.95   $67.90  
  Purchase #5 $245.71   9.767%   $269.7085   $269.71   $269.70   $269.70  
  Purchase #6 $5.28   3.503%   $5.465   $5.47   $5.45   $5.50  
  Purchase #7 $164.80   9.417%   $180.3192   $180.32   $180.30   $180.30  
  7 purchase totals = $841.65       $902.8494   $902.85   $902.85   $902.80