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	$226.43	13.378%	$256.7218	$256.72	$256.70	$256.70
Purchase #2	$187.42	4.776%	$196.3712	$196.37	$196.35	$196.40
Purchase #3	$222.44	3.670%	$230.6035	$230.60	$230.60	$230.60
Purchase #4	$48.32	4.585%	$50.5355	$50.54	$50.55	$50.50
Purchase #5	$64.38	10.535%	$71.1624	$71.16	$71.15	$71.20
Purchase #6	$70.32	12.581%	$79.167	$79.17	$79.15	$79.20
Purchase #7	$236.30	7.460%	$253.928	$253.93	$253.95	$253.90
7 purchase totals =	$1,055.61		$1,138.4894	$1,138.49	$1,138.45	$1,138.50