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	$239.42	13.843%	$272.5629	$272.56	$272.55	$272.60
Purchase #2	$101.43	10.149%	$111.7241	$111.72	$111.70	$111.70
Purchase #3	$29.29	10.621%	$32.4009	$32.40	$32.40	$32.40
Purchase #4	$91.46	5.115%	$96.1382	$96.14	$96.15	$96.10
Purchase #5	$52.32	4.579%	$54.7157	$54.72	$54.70	$54.70
Purchase #6	$192.66	12.794%	$217.3089	$217.31	$217.30	$217.30
Purchase #7	$241.94	5.683%	$255.6895	$255.69	$255.70	$255.70
7 purchase totals =	$948.52		$1,040.5402	$1,040.54	$1,040.50	$1,040.50