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	$175.66	13.592%	$199.5357	$199.54	$199.55	$199.50
Purchase #2	$37.42	3.317%	$38.6612	$38.66	$38.65	$38.70
Purchase #3	$119.39	12.467%	$134.2744	$134.27	$134.25	$134.30
Purchase #4	$187.79	9.422%	$205.4836	$205.48	$205.50	$205.50
Purchase #5	$134.89	13.503%	$153.1042	$153.10	$153.10	$153.10
Purchase #6	$31.92	10.168%	$35.1656	$35.17	$35.15	$35.20
Purchase #7	$224.26	4.194%	$233.6655	$233.67	$233.65	$233.70
7 purchase totals =	$911.33		$999.8902	$999.89	$999.85	$1,000.00