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	$30.63	9.733%	$33.6112	$33.61	$33.60	$33.60
Purchase #2	$245.65	10.504%	$271.4531	$271.45	$271.45	$271.50
Purchase #3	$129.91	9.725%	$142.5437	$142.54	$142.55	$142.50
Purchase #4	$74.95	4.301%	$78.1736	$78.17	$78.15	$78.20
Purchase #5	$64.91	10.466%	$71.7035	$71.70	$71.70	$71.70
Purchase #6	$67.33	11.184%	$74.8602	$74.86	$74.85	$74.90
Purchase #7	$47.81	13.488%	$54.2586	$54.26	$54.25	$54.30
7 purchase totals =	$661.19		$726.6039	$726.59	$726.55	$726.70