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	$115.42	4.303%	$120.3865	$120.39	$120.40	$120.40
Purchase #2	$88.94	4.355%	$92.8133	$92.81	$92.80	$92.80
Purchase #3	$21.31	13.406%	$24.1668	$24.17	$24.15	$24.20
Purchase #4	$217.89	13.396%	$247.0785	$247.08	$247.10	$247.10
Purchase #5	$171.36	7.546%	$184.2908	$184.29	$184.30	$184.30
Purchase #6	$60.61	3.316%	$62.6198	$62.62	$62.60	$62.60
Purchase #7	$100.95	10.543%	$111.5932	$111.59	$111.60	$111.60
7 purchase totals =	$776.48		$842.9489	$842.95	$842.95	$843.00