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	$222.73	13.777%	$253.4155	$253.42	$253.40	$253.40
Purchase #2	$111.96	13.373%	$126.9324	$126.93	$126.95	$126.90
Purchase #3	$214.29	12.162%	$240.3519	$240.35	$240.35	$240.40
Purchase #4	$237.88	11.588%	$265.4455	$265.45	$265.45	$265.40
Purchase #5	$190.61	5.214%	$200.5484	$200.55	$200.55	$200.50
Purchase #6	$134.84	3.380%	$139.3976	$139.40	$139.40	$139.40
Purchase #7	$50.52	8.540%	$54.8344	$54.83	$54.85	$54.80
7 purchase totals =	$1,162.83		$1,280.9257	$1,280.93	$1,280.95	$1,280.80