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	$226.28	7.691%	$243.6832	$243.68	$243.70	$243.70
Purchase #2	$49.56	12.114%	$55.5637	$55.56	$55.55	$55.60
Purchase #3	$39.41	5.579%	$41.6087	$41.61	$41.60	$41.60
Purchase #4	$185.60	10.693%	$205.4462	$205.45	$205.45	$205.40
Purchase #5	$91.75	13.821%	$104.4308	$104.43	$104.45	$104.40
Purchase #6	$184.69	8.759%	$200.867	$200.87	$200.85	$200.90
Purchase #7	$106.72	4.781%	$111.8223	$111.82	$111.80	$111.80
7 purchase totals =	$884.01		$963.4219	$963.42	$963.40	$963.40