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	$10.68	5.179%	$11.2331	$11.23	$11.25	$11.20
Purchase #2	$129.74	9.143%	$141.6021	$141.60	$141.60	$141.60
Purchase #3	$89.63	4.434%	$93.6042	$93.60	$93.60	$93.60
Purchase #4	$91.42	9.457%	$100.0656	$100.07	$100.05	$100.10
Purchase #5	$244.42	4.589%	$255.6364	$255.64	$255.65	$255.60
Purchase #6	$78.59	6.402%	$83.6213	$83.62	$83.60	$83.60
Purchase #7	$157.30	10.601%	$173.9754	$173.98	$174.00	$174.00
7 purchase totals =	$801.78		$859.7381	$859.74	$859.75	$859.70