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	$78.61	13.445%	$89.1791	$89.18	$89.20	$89.20
Purchase #2	$130.43	13.410%	$147.9207	$147.92	$147.90	$147.90
Purchase #3	$146.38	13.772%	$166.5395	$166.54	$166.55	$166.50
Purchase #4	$29.39	9.367%	$32.143	$32.14	$32.15	$32.10
Purchase #5	$79.56	12.849%	$89.7827	$89.78	$89.80	$89.80
Purchase #6	$127.52	8.462%	$138.3107	$138.31	$138.30	$138.30
Purchase #7	$31.43	4.308%	$32.784	$32.78	$32.80	$32.80
7 purchase totals =	$623.32		$696.6597	$696.65	$696.70	$696.60