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	$48.49	13.646%	$55.1069	$55.11	$55.10	$55.10
Purchase #2	$181.91	7.105%	$194.8347	$194.83	$194.85	$194.80
Purchase #3	$34.93	4.640%	$36.5508	$36.55	$36.55	$36.60
Purchase #4	$36.34	9.577%	$39.8203	$39.82	$39.80	$39.80
Purchase #5	$174.47	12.414%	$196.1287	$196.13	$196.15	$196.10
Purchase #6	$122.45	13.733%	$139.2661	$139.27	$139.25	$139.30
Purchase #7	$19.68	5.864%	$20.834	$20.83	$20.85	$20.80
7 purchase totals =	$618.27		$682.5415	$682.54	$682.55	$682.50