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 $97.59   3.752%   $101.2516   $101.25   $101.25   $101.30  
  Purchase #2 $56.60   12.523%   $63.688   $63.69   $63.70   $63.70  
  Purchase #3 $191.73   7.566%   $206.2363   $206.24   $206.25   $206.20  
  Purchase #4 $94.71   3.578%   $98.0987   $98.10   $98.10   $98.10  
  Purchase #5 $114.46   4.561%   $119.6805   $119.68   $119.70   $119.70  
  Purchase #6 $230.78   10.483%   $254.9727   $254.97   $254.95   $255.00  
  Purchase #7 $160.48   7.348%   $172.2721   $172.27   $172.25   $172.30  
  7 purchase totals = $946.35       $1,016.1999   $1,016.20   $1,016.20   $1,016.30