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	$41.83	9.701%	$45.8879	$45.89	$45.90	$45.90
Purchase #2	$43.99	6.435%	$46.8208	$46.82	$46.80	$46.80
Purchase #3	$45.58	9.466%	$49.8946	$49.89	$49.90	$49.90
Purchase #4	$152.87	3.501%	$158.222	$158.22	$158.20	$158.20
Purchase #5	$25.52	10.359%	$28.1636	$28.16	$28.15	$28.20
Purchase #6	$12.56	7.125%	$13.4549	$13.45	$13.45	$13.50
Purchase #7	$238.93	8.130%	$258.355	$258.36	$258.35	$258.40
7 purchase totals =	$561.28		$600.7988	$600.79	$600.75	$600.90