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	$64.75	11.659%	$72.2992	$72.30	$72.30	$72.30
Purchase #2	$101.91	9.670%	$111.7647	$111.76	$111.75	$111.80
Purchase #3	$29.56	10.679%	$32.7167	$32.72	$32.70	$32.70
Purchase #4	$248.75	11.487%	$277.3239	$277.32	$277.30	$277.30
Purchase #5	$88.90	7.384%	$95.4644	$95.46	$95.45	$95.50
Purchase #6	$123.25	4.210%	$128.4388	$128.44	$128.45	$128.40
Purchase #7	$11.65	12.714%	$13.1312	$13.13	$13.15	$13.10
7 purchase totals =	$668.77		$731.1389	$731.13	$731.10	$731.10