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	$61.39	7.726%	$66.133	$66.13	$66.15	$66.10
Purchase #2	$81.40	9.719%	$89.3113	$89.31	$89.30	$89.30
Purchase #3	$27.71	4.699%	$29.0121	$29.01	$29.00	$29.00
Purchase #4	$46.78	6.194%	$49.6776	$49.68	$49.70	$49.70
Purchase #5	$153.34	7.357%	$164.6212	$164.62	$164.60	$164.60
Purchase #6	$55.27	13.234%	$62.5844	$62.58	$62.60	$62.60
Purchase #7	$72.96	12.181%	$81.8473	$81.85	$81.85	$81.80
7 purchase totals =	$498.85		$543.1869	$543.18	$543.20	$543.10