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	$99.65	11.521%	$111.1307	$111.13	$111.15	$111.10
Purchase #2	$205.94	7.753%	$221.9065	$221.91	$221.90	$221.90
Purchase #3	$108.50	8.393%	$117.6064	$117.61	$117.60	$117.60
Purchase #4	$227.46	6.155%	$241.4602	$241.46	$241.45	$241.50
Purchase #5	$220.77	7.154%	$236.5639	$236.56	$236.55	$236.60
Purchase #6	$66.47	3.709%	$68.9354	$68.94	$68.95	$68.90
Purchase #7	$207.80	9.672%	$227.8984	$227.90	$227.90	$227.90
7 purchase totals =	$1,136.59		$1,225.5015	$1,225.51	$1,225.50	$1,225.50