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	$41.78	8.461%	$45.315	$45.32	$45.30	$45.30
Purchase #2	$58.63	12.824%	$66.1487	$66.15	$66.15	$66.10
Purchase #3	$80.64	11.866%	$90.2087	$90.21	$90.20	$90.20
Purchase #4	$85.88	12.485%	$96.6021	$96.60	$96.60	$96.60
Purchase #5	$18.88	7.589%	$20.3128	$20.31	$20.30	$20.30
Purchase #6	$239.38	3.420%	$247.5668	$247.57	$247.55	$247.60
Purchase #7	$223.83	7.818%	$241.329	$241.33	$241.35	$241.30
7 purchase totals =	$749.02		$807.4831	$807.49	$807.45	$807.40