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	$79.58	7.492%	$85.5421	$85.54	$85.55	$85.50
Purchase #2	$51.53	9.795%	$56.5774	$56.58	$56.60	$56.60
Purchase #3	$103.34	7.716%	$111.3137	$111.31	$111.30	$111.30
Purchase #4	$87.33	3.280%	$90.1944	$90.19	$90.20	$90.20
Purchase #5	$60.83	12.232%	$68.2707	$68.27	$68.25	$68.30
Purchase #6	$229.77	9.372%	$251.304	$251.30	$251.30	$251.30
Purchase #7	$15.56	6.657%	$16.5958	$16.60	$16.60	$16.60
7 purchase totals =	$627.94		$679.7981	$679.79	$679.80	$679.80