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	$234.40	13.457%	$265.9432	$265.94	$265.95	$265.90
Purchase #2	$141.65	5.738%	$149.7779	$149.78	$149.80	$149.80
Purchase #3	$10.55	4.109%	$10.9835	$10.98	$11.00	$11.00
Purchase #4	$29.90	12.361%	$33.5959	$33.60	$33.60	$33.60
Purchase #5	$102.49	7.823%	$110.5078	$110.51	$110.50	$110.50
Purchase #6	$103.50	10.821%	$114.6997	$114.70	$114.70	$114.70
Purchase #7	$105.92	5.199%	$111.4268	$111.43	$111.45	$111.40
7 purchase totals =	$728.41		$796.9348	$796.94	$797.00	$796.90