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	$108.78	7.264%	$116.6818	$116.68	$116.70	$116.70
Purchase #2	$66.75	5.823%	$70.6369	$70.64	$70.65	$70.60
Purchase #3	$191.90	9.144%	$209.4473	$209.45	$209.45	$209.40
Purchase #4	$134.32	9.539%	$147.1328	$147.13	$147.15	$147.10
Purchase #5	$124.71	3.351%	$128.889	$128.89	$128.90	$128.90
Purchase #6	$45.90	7.452%	$49.3205	$49.32	$49.30	$49.30
Purchase #7	$74.64	11.812%	$83.4565	$83.46	$83.45	$83.50
7 purchase totals =	$747.00		$805.5648	$805.57	$805.60	$805.50