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	$12.69	6.729%	$13.5439	$13.54	$13.55	$13.50
Purchase #2	$35.59	4.734%	$37.2748	$37.27	$37.25	$37.30
Purchase #3	$72.46	6.403%	$77.0996	$77.10	$77.10	$77.10
Purchase #4	$78.28	12.648%	$88.1809	$88.18	$88.20	$88.20
Purchase #5	$82.91	6.702%	$88.4666	$88.47	$88.45	$88.50
Purchase #6	$135.29	7.239%	$145.0836	$145.08	$145.10	$145.10
Purchase #7	$66.35	6.555%	$70.6992	$70.70	$70.70	$70.70
7 purchase totals =	$483.57		$520.3486	$520.34	$520.35	$520.40