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	$113.43	12.757%	$127.9003	$127.90	$127.90	$127.90
Purchase #2	$51.38	3.443%	$53.149	$53.15	$53.15	$53.10
Purchase #3	$152.91	8.387%	$165.7346	$165.73	$165.75	$165.70
Purchase #4	$72.37	7.847%	$78.0489	$78.05	$78.05	$78.00
Purchase #5	$208.39	5.166%	$219.1554	$219.16	$219.15	$219.20
Purchase #6	$210.65	9.349%	$230.3437	$230.34	$230.35	$230.30
Purchase #7	$203.81	10.441%	$225.0898	$225.09	$225.10	$225.10
7 purchase totals =	$1,012.94		$1,099.4217	$1,099.42	$1,099.45	$1,099.30