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	$11.64	5.440%	$12.2732	$12.27	$12.25	$12.30
Purchase #2	$116.93	9.135%	$127.6116	$127.61	$127.60	$127.60
Purchase #3	$57.48	12.808%	$64.842	$64.84	$64.85	$64.80
Purchase #4	$170.25	11.796%	$190.3327	$190.33	$190.35	$190.30
Purchase #5	$153.87	7.342%	$165.1671	$165.17	$165.15	$165.20
Purchase #6	$143.83	8.779%	$156.4568	$156.46	$156.45	$156.50
Purchase #7	$16.30	10.588%	$18.0258	$18.03	$18.05	$18.00
7 purchase totals =	$670.30		$734.7092	$734.71	$734.70	$734.70