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	$144.48	5.159%	$151.9337	$151.93	$151.95	$151.90
Purchase #2	$49.38	11.134%	$54.878	$54.88	$54.90	$54.90
Purchase #3	$20.42	3.179%	$21.0692	$21.07	$21.05	$21.10
Purchase #4	$132.58	13.431%	$150.3868	$150.39	$150.40	$150.40
Purchase #5	$22.70	7.558%	$24.4157	$24.42	$24.40	$24.40
Purchase #6	$122.60	13.819%	$139.5421	$139.54	$139.55	$139.50
Purchase #7	$91.61	6.566%	$97.6251	$97.63	$97.65	$97.60
7 purchase totals =	$583.77		$639.8506	$639.86	$639.90	$639.80