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	$35.62	5.273%	$37.4982	$37.50	$37.50	$37.50
Purchase #2	$226.89	5.364%	$239.0604	$239.06	$239.05	$239.10
Purchase #3	$80.65	11.780%	$90.1506	$90.15	$90.15	$90.20
Purchase #4	$21.94	4.109%	$22.8415	$22.84	$22.85	$22.80
Purchase #5	$31.37	9.322%	$34.2943	$34.29	$34.30	$34.30
Purchase #6	$79.43	12.200%	$89.1205	$89.12	$89.10	$89.10
Purchase #7	$194.51	10.185%	$214.3208	$214.32	$214.30	$214.30
7 purchase totals =	$670.41		$727.2863	$727.28	$727.25	$727.30