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	$142.32	12.842%	$160.5967	$160.60	$160.60	$160.60
Purchase #2	$148.39	3.104%	$152.996	$153.00	$153.00	$153.00
Purchase #3	$100.46	7.116%	$107.6087	$107.61	$107.60	$107.60
Purchase #4	$77.70	11.252%	$86.4428	$86.44	$86.45	$86.40
Purchase #5	$30.61	5.509%	$32.2963	$32.30	$32.30	$32.30
Purchase #6	$155.98	7.236%	$167.2667	$167.27	$167.25	$167.30
Purchase #7	$73.85	6.203%	$78.4309	$78.43	$78.45	$78.40
7 purchase totals =	$729.31		$785.6381	$785.65	$785.65	$785.60