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	$49.86	12.422%	$56.0536	$56.05	$56.05	$56.10
Purchase #2	$162.59	11.163%	$180.7399	$180.74	$180.75	$180.70
Purchase #3	$8.52	11.525%	$9.5019	$9.50	$9.50	$9.50
Purchase #4	$61.41	9.391%	$67.177	$67.18	$67.20	$67.20
Purchase #5	$231.27	9.540%	$253.3332	$253.33	$253.35	$253.30
Purchase #6	$85.29	4.469%	$89.1016	$89.10	$89.10	$89.10
Purchase #7	$209.78	9.616%	$229.9524	$229.95	$229.95	$230.00
7 purchase totals =	$808.72		$885.8596	$885.85	$885.90	$885.90