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	$85.73	4.306%	$89.4215	$89.42	$89.40	$89.40
Purchase #2	$183.61	4.123%	$191.1802	$191.18	$191.20	$191.20
Purchase #3	$54.26	9.208%	$59.2563	$59.26	$59.25	$59.30
Purchase #4	$14.29	8.746%	$15.5398	$15.54	$15.55	$15.50
Purchase #5	$45.35	7.127%	$48.5821	$48.58	$48.60	$48.60
Purchase #6	$145.84	3.613%	$151.1092	$151.11	$151.10	$151.10
Purchase #7	$5.85	13.386%	$6.6331	$6.63	$6.65	$6.60
7 purchase totals =	$534.93		$561.7222	$561.72	$561.75	$561.70