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	$66.50	3.343%	$68.7231	$68.72	$68.70	$68.70
Purchase #2	$175.64	11.726%	$196.2355	$196.24	$196.25	$196.20
Purchase #3	$61.48	7.601%	$66.1531	$66.15	$66.15	$66.20
Purchase #4	$13.75	6.171%	$14.5985	$14.60	$14.60	$14.60
Purchase #5	$118.70	7.459%	$127.5538	$127.55	$127.55	$127.60
Purchase #6	$173.73	11.225%	$193.2312	$193.23	$193.25	$193.20
Purchase #7	$162.80	6.576%	$173.5057	$173.51	$173.50	$173.50
7 purchase totals =	$772.60		$840.0009	$840.00	$840.00	$840.00