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	$97.86	3.128%	$100.9211	$100.92	$100.90	$100.90
Purchase #2	$118.27	4.130%	$123.1546	$123.15	$123.15	$123.20
Purchase #3	$225.52	5.844%	$238.6994	$238.70	$238.70	$238.70
Purchase #4	$73.89	3.261%	$76.2996	$76.30	$76.30	$76.30
Purchase #5	$54.99	12.353%	$61.7829	$61.78	$61.80	$61.80
Purchase #6	$56.82	4.784%	$59.5383	$59.54	$59.55	$59.50
Purchase #7	$233.49	9.849%	$256.4864	$256.49	$256.50	$256.50
7 purchase totals =	$860.84		$916.8823	$916.88	$916.90	$916.90