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	$80.77	10.204%	$89.0118	$89.01	$89.00	$89.00
Purchase #2	$162.84	9.454%	$178.2349	$178.23	$178.25	$178.20
Purchase #3	$51.84	9.687%	$56.8617	$56.86	$56.85	$56.90
Purchase #4	$14.37	9.687%	$15.762	$15.76	$15.75	$15.80
Purchase #5	$241.50	8.680%	$262.4622	$262.46	$262.45	$262.50
Purchase #6	$34.80	7.276%	$37.332	$37.33	$37.35	$37.30
Purchase #7	$248.60	11.205%	$276.4556	$276.46	$276.45	$276.50
7 purchase totals =	$834.72		$916.1202	$916.11	$916.10	$916.20