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	$146.28	13.772%	$166.4257	$166.43	$166.45	$166.40
Purchase #2	$111.89	10.298%	$123.4124	$123.41	$123.40	$123.40
Purchase #3	$220.50	12.840%	$248.8122	$248.81	$248.80	$248.80
Purchase #4	$99.83	7.418%	$107.2354	$107.24	$107.25	$107.20
Purchase #5	$12.42	9.111%	$13.5516	$13.55	$13.55	$13.60
Purchase #6	$13.49	4.502%	$14.0973	$14.10	$14.10	$14.10
Purchase #7	$95.52	7.533%	$102.7155	$102.72	$102.70	$102.70
7 purchase totals =	$699.93		$776.2501	$776.26	$776.25	$776.20