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 $30.76   6.172%   $32.6585   $32.66   $32.65   $32.70  
  Purchase #2 $136.39   9.174%   $148.9024   $148.90   $148.90   $148.90  
  Purchase #3 $118.74   9.348%   $129.8398   $129.84   $129.85   $129.80  
  Purchase #4 $248.71   9.312%   $271.8699   $271.87   $271.85   $271.90  
  Purchase #5 $231.63   8.268%   $250.7812   $250.78   $250.80   $250.80  
  Purchase #6 $116.66   6.378%   $124.1006   $124.10   $124.10   $124.10  
  Purchase #7 $136.88   11.283%   $152.3242   $152.32   $152.30   $152.30  
  7 purchase totals = $1,019.77       $1,110.4766   $1,110.47   $1,110.45   $1,110.50