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	$12.25	5.417%	$12.9136	$12.91	$12.90	$12.90
Purchase #2	$138.60	9.219%	$151.3775	$151.38	$151.40	$151.40
Purchase #3	$184.93	7.859%	$199.4636	$199.46	$199.45	$199.50
Purchase #4	$44.92	12.746%	$50.6455	$50.65	$50.65	$50.60
Purchase #5	$188.45	6.102%	$199.9492	$199.95	$199.95	$199.90
Purchase #6	$247.37	12.162%	$277.4551	$277.46	$277.45	$277.50
Purchase #7	$196.86	8.773%	$214.1305	$214.13	$214.15	$214.10
7 purchase totals =	$1,013.38		$1,105.9350	$1,105.94	$1,105.95	$1,105.90