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	$82.84	6.405%	$88.1459	$88.15	$88.15	$88.10
Purchase #2	$229.66	13.351%	$260.3219	$260.32	$260.30	$260.30
Purchase #3	$138.32	4.392%	$144.395	$144.40	$144.40	$144.40
Purchase #4	$185.94	10.401%	$205.2796	$205.28	$205.30	$205.30
Purchase #5	$160.88	4.717%	$168.4687	$168.47	$168.45	$168.50
Purchase #6	$49.83	13.575%	$56.5944	$56.59	$56.60	$56.60
Purchase #7	$241.53	12.747%	$272.3178	$272.32	$272.30	$272.30
7 purchase totals =	$1,089.00		$1,195.5233	$1,195.53	$1,195.50	$1,195.50