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	$109.62	7.267%	$117.5861	$117.59	$117.60	$117.60
Purchase #2	$230.35	12.472%	$259.0793	$259.08	$259.10	$259.10
Purchase #3	$241.89	4.835%	$253.5854	$253.59	$253.60	$253.60
Purchase #4	$214.51	12.635%	$241.6133	$241.61	$241.60	$241.60
Purchase #5	$71.77	13.714%	$81.6125	$81.61	$81.60	$81.60
Purchase #6	$92.76	7.408%	$99.6317	$99.63	$99.65	$99.60
Purchase #7	$228.30	8.180%	$246.9749	$246.97	$246.95	$247.00
7 purchase totals =	$1,189.20		$1,300.0832	$1,300.08	$1,300.10	$1,300.10