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	$248.74	11.530%	$277.4197	$277.42	$277.40	$277.40
Purchase #2	$145.42	4.371%	$151.7763	$151.78	$151.80	$151.80
Purchase #3	$62.80	3.696%	$65.1211	$65.12	$65.10	$65.10
Purchase #4	$82.39	10.196%	$90.7905	$90.79	$90.80	$90.80
Purchase #5	$18.64	8.525%	$20.2291	$20.23	$20.25	$20.20
Purchase #6	$84.61	5.533%	$89.2915	$89.29	$89.30	$89.30
Purchase #7	$130.53	11.107%	$145.028	$145.03	$145.05	$145.00
7 purchase totals =	$773.13		$839.6562	$839.66	$839.70	$839.60