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 $241.54   10.663%   $267.2954   $267.30   $267.30   $267.30  
  Purchase #2 $114.83   3.659%   $119.0316   $119.03   $119.05   $119.00  
  Purchase #3 $159.41   7.422%   $171.2414   $171.24   $171.25   $171.20  
  Purchase #4 $212.67   7.874%   $229.4156   $229.42   $229.40   $229.40  
  Purchase #5 $91.28   11.493%   $101.7708   $101.77   $101.75   $101.80  
  Purchase #6 $8.95   10.723%   $9.9097   $9.91   $9.90   $9.90  
  Purchase #7 $52.63   8.146%   $56.9172   $56.92   $56.90   $56.90  
  7 purchase totals = $881.31       $955.5817   $955.59   $955.55   $955.50