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	$38.45	12.627%	$43.3051	$43.31	$43.30	$43.30
Purchase #2	$160.93	11.395%	$179.268	$179.27	$179.25	$179.30
Purchase #3	$11.57	7.556%	$12.4442	$12.44	$12.45	$12.40
Purchase #4	$102.45	3.358%	$105.8903	$105.89	$105.90	$105.90
Purchase #5	$89.41	10.757%	$99.0278	$99.03	$99.05	$99.00
Purchase #6	$93.79	13.208%	$106.1778	$106.18	$106.20	$106.20
Purchase #7	$105.72	10.842%	$117.1822	$117.18	$117.20	$117.20
7 purchase totals =	$602.32		$663.2954	$663.30	$663.35	$663.30