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 $249.75   6.542%   $266.0886   $266.09   $266.10   $266.10  
  Purchase #2 $172.71   13.169%   $195.4542   $195.45   $195.45   $195.50  
  Purchase #3 $239.94   9.352%   $262.3792   $262.38   $262.40   $262.40  
  Purchase #4 $95.44   10.513%   $105.4736   $105.47   $105.45   $105.50  
  Purchase #5 $234.38   13.155%   $265.2127   $265.21   $265.20   $265.20  
  Purchase #6 $76.90   13.639%   $87.3884   $87.39   $87.40   $87.40  
  Purchase #7 $223.61   4.767%   $234.2695   $234.27   $234.25   $234.30  
  7 purchase totals = $1,292.73       $1,416.2662   $1,416.26   $1,416.25   $1,416.40