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	$166.32	13.175%	$188.2327	$188.23	$188.25	$188.20
Purchase #2	$61.35	8.567%	$66.6059	$66.61	$66.60	$66.60
Purchase #3	$60.74	6.510%	$64.6942	$64.69	$64.70	$64.70
Purchase #4	$53.31	4.218%	$55.5586	$55.56	$55.55	$55.60
Purchase #5	$49.85	13.553%	$56.6062	$56.61	$56.60	$56.60
Purchase #6	$175.90	7.700%	$189.4443	$189.44	$189.45	$189.40
Purchase #7	$62.82	11.102%	$69.7943	$69.79	$69.80	$69.80
7 purchase totals =	$630.29		$690.9362	$690.93	$690.95	$690.90