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	$133.94	10.699%	$148.2702	$148.27	$148.25	$148.30
Purchase #2	$97.93	8.133%	$105.8946	$105.89	$105.90	$105.90
Purchase #3	$40.29	8.205%	$43.5958	$43.60	$43.60	$43.60
Purchase #4	$77.60	7.805%	$83.6567	$83.66	$83.65	$83.70
Purchase #5	$152.56	4.541%	$159.4877	$159.49	$159.50	$159.50
Purchase #6	$96.92	5.626%	$102.3727	$102.37	$102.35	$102.40
Purchase #7	$172.67	13.313%	$195.6576	$195.66	$195.65	$195.70
7 purchase totals =	$771.91		$838.9353	$838.94	$838.90	$839.10