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	$102.82	11.677%	$114.8263	$114.83	$114.85	$114.80
Purchase #2	$60.27	6.615%	$64.2569	$64.26	$64.25	$64.30
Purchase #3	$168.28	9.642%	$184.5056	$184.51	$184.50	$184.50
Purchase #4	$224.91	11.719%	$251.2672	$251.27	$251.25	$251.30
Purchase #5	$119.73	6.568%	$127.5939	$127.59	$127.60	$127.60
Purchase #6	$29.65	10.197%	$32.6734	$32.67	$32.65	$32.70
Purchase #7	$106.74	9.414%	$116.7885	$116.79	$116.80	$116.80
7 purchase totals =	$812.40		$891.9118	$891.92	$891.90	$892.00