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	$52.96	7.607%	$56.9887	$56.99	$57.00	$57.00
Purchase #2	$101.96	3.579%	$105.6091	$105.61	$105.60	$105.60
Purchase #3	$159.45	8.141%	$172.4308	$172.43	$172.45	$172.40
Purchase #4	$79.70	4.487%	$83.2761	$83.28	$83.30	$83.30
Purchase #5	$25.59	10.703%	$28.3289	$28.33	$28.35	$28.30
Purchase #6	$127.93	7.111%	$137.0271	$137.03	$137.05	$137.00
Purchase #7	$88.97	7.160%	$95.3403	$95.34	$95.35	$95.30
7 purchase totals =	$636.56		$679.0010	$679.01	$679.10	$678.90