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 $57.91   5.548%   $61.1228   $61.12   $61.10   $61.10  
  Purchase #2 $98.47   4.448%   $102.8499   $102.85   $102.85   $102.80  
  Purchase #3 $242.83   9.301%   $265.4156   $265.42   $265.40   $265.40  
  Purchase #4 $151.64   13.144%   $171.5716   $171.57   $171.55   $171.60  
  Purchase #5 $234.41   11.321%   $260.9476   $260.95   $260.95   $260.90  
  Purchase #6 $114.63   9.323%   $125.317   $125.32   $125.30   $125.30  
  Purchase #7 $226.73   11.214%   $252.1555   $252.16   $252.15   $252.20  
  7 purchase totals = $1,126.62       $1,239.3800   $1,239.39   $1,239.30   $1,239.30