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	$157.56	6.748%	$168.1921	$168.19	$168.20	$168.20
Purchase #2	$147.66	11.863%	$165.1769	$165.18	$165.20	$165.20
Purchase #3	$19.92	12.536%	$22.4172	$22.42	$22.40	$22.40
Purchase #4	$43.75	8.119%	$47.3021	$47.30	$47.30	$47.30
Purchase #5	$84.86	5.613%	$89.6232	$89.62	$89.60	$89.60
Purchase #6	$138.96	8.760%	$151.1329	$151.13	$151.15	$151.10
Purchase #7	$56.25	11.667%	$62.8127	$62.81	$62.80	$62.80
7 purchase totals =	$648.96		$706.6571	$706.65	$706.65	$706.60