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	$15.86	10.281%	$17.4906	$17.49	$17.50	$17.50
Purchase #2	$229.37	10.758%	$254.0456	$254.05	$254.05	$254.00
Purchase #3	$99.73	4.551%	$104.2687	$104.27	$104.25	$104.30
Purchase #4	$172.86	5.734%	$182.7718	$182.77	$182.75	$182.80
Purchase #5	$202.41	13.233%	$229.1949	$229.19	$229.20	$229.20
Purchase #6	$103.72	7.249%	$111.2387	$111.24	$111.25	$111.20
Purchase #7	$96.67	8.464%	$104.8521	$104.85	$104.85	$104.90
7 purchase totals =	$920.62		$1,003.8624	$1,003.86	$1,003.85	$1,003.90