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	$241.32	13.411%	$273.6834	$273.68	$273.70	$273.70
Purchase #2	$100.90	12.225%	$113.235	$113.24	$113.25	$113.20
Purchase #3	$113.29	3.850%	$117.6517	$117.65	$117.65	$117.70
Purchase #4	$136.83	4.762%	$143.3458	$143.35	$143.35	$143.30
Purchase #5	$223.81	5.187%	$235.419	$235.42	$235.40	$235.40
Purchase #6	$156.71	11.171%	$174.2161	$174.22	$174.20	$174.20
Purchase #7	$173.41	13.373%	$196.6001	$196.60	$196.60	$196.60
7 purchase totals =	$1,146.27		$1,254.1511	$1,254.16	$1,254.15	$1,254.10