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	$14.81	4.638%	$15.4969	$15.50	$15.50	$15.50
Purchase #2	$58.49	5.845%	$61.9087	$61.91	$61.90	$61.90
Purchase #3	$208.70	13.664%	$237.2168	$237.22	$237.20	$237.20
Purchase #4	$96.46	4.336%	$100.6425	$100.64	$100.65	$100.60
Purchase #5	$20.29	12.629%	$22.8524	$22.85	$22.85	$22.90
Purchase #6	$134.90	8.528%	$146.4043	$146.40	$146.40	$146.40
Purchase #7	$48.66	5.530%	$51.3509	$51.35	$51.35	$51.40
7 purchase totals =	$582.31		$635.8725	$635.87	$635.85	$635.90