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	$28.89	7.789%	$31.1402	$31.14	$31.15	$31.10
Purchase #2	$26.39	5.639%	$27.8781	$27.88	$27.90	$27.90
Purchase #3	$101.43	3.846%	$105.331	$105.33	$105.35	$105.30
Purchase #4	$201.31	11.267%	$223.9916	$223.99	$224.00	$224.00
Purchase #5	$63.61	4.739%	$66.6245	$66.62	$66.60	$66.60
Purchase #6	$43.33	12.376%	$48.6925	$48.69	$48.70	$48.70
Purchase #7	$26.27	12.696%	$29.6052	$29.61	$29.60	$29.60
7 purchase totals =	$491.23		$533.2631	$533.26	$533.30	$533.20