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	$62.42	6.311%	$66.3593	$66.36	$66.35	$66.40
Purchase #2	$23.25	4.675%	$24.3369	$24.34	$24.35	$24.30
Purchase #3	$155.46	7.287%	$166.7884	$166.79	$166.80	$166.80
Purchase #4	$74.79	10.152%	$82.3827	$82.38	$82.40	$82.40
Purchase #5	$69.45	10.676%	$76.8645	$76.86	$76.85	$76.90
Purchase #6	$170.83	11.361%	$190.238	$190.24	$190.25	$190.20
Purchase #7	$201.55	6.795%	$215.2453	$215.25	$215.25	$215.20
7 purchase totals =	$757.75		$822.2151	$822.22	$822.25	$822.20