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	$26.58	10.837%	$29.4605	$29.46	$29.45	$29.50
Purchase #2	$139.33	13.498%	$158.1368	$158.14	$158.15	$158.10
Purchase #3	$151.54	7.499%	$162.904	$162.90	$162.90	$162.90
Purchase #4	$222.46	12.577%	$250.4388	$250.44	$250.45	$250.40
Purchase #5	$21.31	7.603%	$22.9302	$22.93	$22.95	$22.90
Purchase #6	$54.47	6.109%	$57.7976	$57.80	$57.80	$57.80
Purchase #7	$52.60	5.781%	$55.6408	$55.64	$55.65	$55.60
7 purchase totals =	$668.29		$737.3087	$737.31	$737.35	$737.20