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	$126.56	13.358%	$143.4659	$143.47	$143.45	$143.50
Purchase #2	$198.36	10.128%	$218.4499	$218.45	$218.45	$218.40
Purchase #3	$155.43	12.510%	$174.8743	$174.87	$174.85	$174.90
Purchase #4	$172.96	7.208%	$185.427	$185.43	$185.45	$185.40
Purchase #5	$78.73	11.286%	$87.6155	$87.62	$87.60	$87.60
Purchase #6	$144.45	11.172%	$160.588	$160.59	$160.60	$160.60
Purchase #7	$150.51	10.639%	$166.5228	$166.52	$166.50	$166.50
7 purchase totals =	$1,027.00		$1,136.9434	$1,136.95	$1,136.90	$1,136.90