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	$145.95	4.521%	$152.5484	$152.55	$152.55	$152.50
Purchase #2	$117.37	9.397%	$128.3993	$128.40	$128.40	$128.40
Purchase #3	$243.79	10.381%	$269.0978	$269.10	$269.10	$269.10
Purchase #4	$144.42	7.832%	$155.731	$155.73	$155.75	$155.70
Purchase #5	$47.35	7.672%	$50.9827	$50.98	$51.00	$51.00
Purchase #6	$89.25	5.831%	$94.4542	$94.45	$94.45	$94.50
Purchase #7	$44.77	12.335%	$50.2924	$50.29	$50.30	$50.30
7 purchase totals =	$832.90		$901.5058	$901.50	$901.55	$901.50