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 $60.56   12.529%   $68.1476   $68.15   $68.15   $68.10  
  Purchase #2 $107.36   6.415%   $114.2471   $114.25   $114.25   $114.20  
  Purchase #3 $159.69   5.184%   $167.9683   $167.97   $167.95   $168.00  
  Purchase #4 $249.75   6.782%   $266.688   $266.69   $266.70   $266.70  
  Purchase #5 $189.76   11.188%   $210.9903   $210.99   $211.00   $211.00  
  Purchase #6 $240.27   8.684%   $261.135   $261.14   $261.15   $261.10  
  Purchase #7 $143.69   9.598%   $157.4814   $157.48   $157.50   $157.50  
  7 purchase totals = $1,151.08       $1,246.6577   $1,246.67   $1,246.70   $1,246.60