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 $249.89   7.622%   $268.9366   $268.94   $268.95   $268.90  
  Purchase #2 $128.60   9.835%   $141.2478   $141.25   $141.25   $141.20  
  Purchase #3 $225.85   11.854%   $252.6223   $252.62   $252.60   $252.60  
  Purchase #4 $10.30   4.609%   $10.7747   $10.77   $10.75   $10.80  
  Purchase #5 $8.96   5.860%   $9.4851   $9.49   $9.50   $9.50  
  Purchase #6 $242.97   8.241%   $262.9932   $262.99   $263.00   $263.00  
  Purchase #7 $6.51   5.306%   $6.8554   $6.86   $6.85   $6.90  
  7 purchase totals = $873.08       $952.9151   $952.92   $952.90   $952.90