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	$13.30	5.824%	$14.0746	$14.07	$14.05	$14.10
Purchase #2	$46.90	11.808%	$52.438	$52.44	$52.45	$52.40
Purchase #3	$89.31	6.677%	$95.2732	$95.27	$95.25	$95.30
Purchase #4	$113.55	13.701%	$129.1075	$129.11	$129.10	$129.10
Purchase #5	$70.31	3.624%	$72.858	$72.86	$72.85	$72.90
Purchase #6	$208.37	10.150%	$229.5196	$229.52	$229.50	$229.50
Purchase #7	$41.81	11.610%	$46.6641	$46.66	$46.65	$46.70
7 purchase totals =	$583.55		$639.9350	$639.93	$639.85	$640.00