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	$231.56	8.238%	$250.6359	$250.64	$250.65	$250.60
Purchase #2	$206.54	9.235%	$225.614	$225.61	$225.60	$225.60
Purchase #3	$247.82	12.840%	$279.6401	$279.64	$279.65	$279.60
Purchase #4	$50.66	7.200%	$54.3075	$54.31	$54.30	$54.30
Purchase #5	$140.61	12.852%	$158.6812	$158.68	$158.70	$158.70
Purchase #6	$126.76	4.496%	$132.4591	$132.46	$132.45	$132.50
Purchase #7	$218.59	6.861%	$233.5875	$233.59	$233.60	$233.60
7 purchase totals =	$1,222.54		$1,334.9253	$1,334.93	$1,334.95	$1,334.90