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	$23.68	3.184%	$24.434	$24.43	$24.45	$24.40
Purchase #2	$54.88	3.131%	$56.5983	$56.60	$56.60	$56.60
Purchase #3	$50.57	9.139%	$55.1916	$55.19	$55.20	$55.20
Purchase #4	$178.34	5.313%	$187.8152	$187.82	$187.80	$187.80
Purchase #5	$121.60	4.665%	$127.2726	$127.27	$127.25	$127.30
Purchase #6	$37.28	11.869%	$41.7048	$41.70	$41.70	$41.70
Purchase #7	$126.75	8.806%	$137.9116	$137.91	$137.90	$137.90
7 purchase totals =	$593.10		$630.9281	$630.92	$630.90	$630.90