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	$246.52	6.609%	$262.8125	$262.81	$262.80	$262.80
Purchase #2	$28.32	13.498%	$32.1426	$32.14	$32.15	$32.10
Purchase #3	$54.42	3.812%	$56.4945	$56.49	$56.50	$56.50
Purchase #4	$50.77	5.533%	$53.5791	$53.58	$53.60	$53.60
Purchase #5	$97.50	9.599%	$106.859	$106.86	$106.85	$106.90
Purchase #6	$107.27	10.819%	$118.8755	$118.88	$118.90	$118.90
Purchase #7	$32.41	11.479%	$36.1303	$36.13	$36.15	$36.10
7 purchase totals =	$617.21		$666.8935	$666.89	$666.95	$666.90