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	$239.81	6.551%	$255.52	$255.52	$255.50	$255.50
Purchase #2	$219.28	5.170%	$230.6168	$230.62	$230.60	$230.60
Purchase #3	$217.72	12.185%	$244.2492	$244.25	$244.25	$244.20
Purchase #4	$250.67	3.373%	$259.1251	$259.13	$259.15	$259.10
Purchase #5	$46.88	12.800%	$52.8806	$52.88	$52.90	$52.90
Purchase #6	$8.85	6.336%	$9.4107	$9.41	$9.40	$9.40
Purchase #7	$93.76	6.529%	$99.8816	$99.88	$99.90	$99.90
7 purchase totals =	$1,076.97		$1,151.6840	$1,151.69	$1,151.70	$1,151.60