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 $92.33   12.379%   $103.7595   $103.76   $103.75   $103.80  
  Purchase #2 $175.49   10.303%   $193.5707   $193.57   $193.55   $193.60  
  Purchase #3 $227.68   3.737%   $236.1884   $236.19   $236.20   $236.20  
  Purchase #4 $216.26   8.407%   $234.441   $234.44   $234.45   $234.40  
  Purchase #5 $250.67   4.327%   $261.5165   $261.52   $261.50   $261.50  
  Purchase #6 $171.77   13.492%   $194.9452   $194.95   $194.95   $194.90  
  Purchase #7 $15.55   12.106%   $17.4325   $17.43   $17.45   $17.40  
  7 purchase totals = $1,149.75       $1,241.8538   $1,241.86   $1,241.85   $1,241.80