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	$58.39	11.179%	$64.9174	$64.92	$64.90	$64.90
Purchase #2	$80.26	12.487%	$90.2821	$90.28	$90.30	$90.30
Purchase #3	$54.59	7.812%	$58.8546	$58.85	$58.85	$58.90
Purchase #4	$64.75	11.168%	$71.9813	$71.98	$72.00	$72.00
Purchase #5	$146.86	7.640%	$158.0801	$158.08	$158.10	$158.10
Purchase #6	$25.27	6.536%	$26.9216	$26.92	$26.90	$26.90
Purchase #7	$107.42	5.719%	$113.5633	$113.56	$113.55	$113.60
7 purchase totals =	$537.54		$584.6004	$584.59	$584.60	$584.70