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	$49.77	9.697%	$54.5962	$54.60	$54.60	$54.60
Purchase #2	$226.25	12.569%	$254.6874	$254.69	$254.70	$254.70
Purchase #3	$75.75	3.588%	$78.4679	$78.47	$78.45	$78.50
Purchase #4	$41.48	12.748%	$46.7679	$46.77	$46.75	$46.80
Purchase #5	$114.27	10.394%	$126.1472	$126.15	$126.15	$126.10
Purchase #6	$51.32	8.299%	$55.579	$55.58	$55.60	$55.60
Purchase #7	$242.98	8.223%	$262.9602	$262.96	$262.95	$263.00
7 purchase totals =	$801.82		$879.2058	$879.22	$879.20	$879.30