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	$246.81	9.146%	$269.3832	$269.38	$269.40	$269.40
Purchase #2	$142.25	6.353%	$151.2871	$151.29	$151.30	$151.30
Purchase #3	$26.55	7.650%	$28.5811	$28.58	$28.60	$28.60
Purchase #4	$127.30	5.564%	$134.383	$134.38	$134.40	$134.40
Purchase #5	$193.89	7.350%	$208.1409	$208.14	$208.15	$208.10
Purchase #6	$40.77	12.403%	$45.8267	$45.83	$45.85	$45.80
Purchase #7	$102.36	3.320%	$105.7584	$105.76	$105.75	$105.80
7 purchase totals =	$879.93		$943.3604	$943.36	$943.45	$943.40