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	$78.36	5.479%	$82.6533	$82.65	$82.65	$82.70
Purchase #2	$122.85	7.710%	$132.3217	$132.32	$132.30	$132.30
Purchase #3	$85.28	4.483%	$89.1031	$89.10	$89.10	$89.10
Purchase #4	$94.28	6.463%	$100.3733	$100.37	$100.35	$100.40
Purchase #5	$136.77	9.784%	$150.1516	$150.15	$150.15	$150.20
Purchase #6	$25.80	4.601%	$26.9871	$26.99	$27.00	$27.00
Purchase #7	$144.39	8.307%	$156.3845	$156.38	$156.40	$156.40
7 purchase totals =	$687.73		$737.9746	$737.96	$737.95	$738.10