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 $230.93   13.682%   $262.5258   $262.53   $262.55   $262.50  
  Purchase #2 $66.77   10.223%   $73.5959   $73.60   $73.60   $73.60  
  Purchase #3 $117.28   5.721%   $123.9896   $123.99   $124.00   $124.00  
  Purchase #4 $151.98   6.186%   $161.3815   $161.38   $161.40   $161.40  
  Purchase #5 $70.32   9.362%   $76.9034   $76.90   $76.90   $76.90  
  Purchase #6 $112.27   7.577%   $120.7767   $120.78   $120.80   $120.80  
  Purchase #7 $60.44   4.869%   $63.3828   $63.38   $63.40   $63.40  
  7 purchase totals = $809.99       $882.5557   $882.56   $882.65   $882.60