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	$120.49	6.680%	$128.5387	$128.54	$128.55	$128.50
Purchase #2	$210.88	12.642%	$237.5394	$237.54	$237.55	$237.50
Purchase #3	$132.42	3.183%	$136.6349	$136.63	$136.65	$136.60
Purchase #4	$50.46	8.129%	$54.5619	$54.56	$54.55	$54.60
Purchase #5	$142.88	13.404%	$162.0316	$162.03	$162.05	$162.00
Purchase #6	$18.54	13.726%	$21.0848	$21.08	$21.10	$21.10
Purchase #7	$142.52	5.866%	$150.8802	$150.88	$150.90	$150.90
7 purchase totals =	$818.19		$891.2715	$891.26	$891.35	$891.20