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	$10.31	5.632%	$10.8907	$10.89	$10.90	$10.90
Purchase #2	$111.75	6.374%	$118.8729	$118.87	$118.85	$118.90
Purchase #3	$104.66	7.741%	$112.7617	$112.76	$112.75	$112.80
Purchase #4	$228.40	13.306%	$258.7909	$258.79	$258.80	$258.80
Purchase #5	$213.32	13.165%	$241.4036	$241.40	$241.40	$241.40
Purchase #6	$227.64	12.301%	$255.642	$255.64	$255.65	$255.60
Purchase #7	$220.43	3.784%	$228.7711	$228.77	$228.75	$228.80
7 purchase totals =	$1,116.51		$1,227.1329	$1,227.12	$1,227.10	$1,227.20