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	$238.95	13.609%	$271.4687	$271.47	$271.45	$271.50
Purchase #2	$102.35	5.216%	$107.6886	$107.69	$107.70	$107.70
Purchase #3	$172.53	11.679%	$192.6798	$192.68	$192.70	$192.70
Purchase #4	$64.28	12.802%	$72.5091	$72.51	$72.50	$72.50
Purchase #5	$112.54	3.596%	$116.5869	$116.59	$116.60	$116.60
Purchase #6	$227.65	10.184%	$250.8339	$250.83	$250.85	$250.80
Purchase #7	$233.87	5.380%	$246.4522	$246.45	$246.45	$246.50
7 purchase totals =	$1,152.17		$1,258.2192	$1,258.22	$1,258.25	$1,258.30