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	$117.76	4.815%	$123.4301	$123.43	$123.45	$123.40
Purchase #2	$235.96	3.470%	$244.1478	$244.15	$244.15	$244.10
Purchase #3	$213.87	12.572%	$240.7577	$240.76	$240.75	$240.80
Purchase #4	$183.88	11.415%	$204.8699	$204.87	$204.85	$204.90
Purchase #5	$146.33	13.156%	$165.5812	$165.58	$165.60	$165.60
Purchase #6	$111.87	7.393%	$120.1405	$120.14	$120.15	$120.10
Purchase #7	$38.27	8.423%	$41.4935	$41.49	$41.50	$41.50
7 purchase totals =	$1,047.94		$1,140.4207	$1,140.42	$1,140.45	$1,140.40