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	$120.57	6.727%	$128.6807	$128.68	$128.70	$128.70
Purchase #2	$127.34	4.495%	$133.0639	$133.06	$133.05	$133.10
Purchase #3	$86.95	3.601%	$90.0811	$90.08	$90.10	$90.10
Purchase #4	$200.39	12.702%	$225.8435	$225.84	$225.85	$225.80
Purchase #5	$87.50	13.348%	$99.1795	$99.18	$99.20	$99.20
Purchase #6	$137.72	13.400%	$156.1745	$156.17	$156.15	$156.20
Purchase #7	$35.56	10.452%	$39.2767	$39.28	$39.30	$39.30
7 purchase totals =	$796.03		$872.2999	$872.29	$872.35	$872.40