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 $89.84   5.309%   $94.6096   $94.61   $94.60   $94.60  
  Purchase #2 $247.95   3.674%   $257.0597   $257.06   $257.05   $257.10  
  Purchase #3 $97.26   6.581%   $103.6607   $103.66   $103.65   $103.70  
  Purchase #4 $248.94   4.862%   $261.0435   $261.04   $261.05   $261.00  
  Purchase #5 $125.84   5.788%   $133.1236   $133.12   $133.10   $133.10  
  Purchase #6 $175.93   9.242%   $192.1895   $192.19   $192.20   $192.20  
  Purchase #7 $230.26   12.692%   $259.4846   $259.48   $259.50   $259.50  
  7 purchase totals = $1,216.02       $1,301.1712   $1,301.16   $1,301.15   $1,301.20