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	$155.28	6.767%	$165.7878	$165.79	$165.80	$165.80
Purchase #2	$199.68	9.446%	$218.5418	$218.54	$218.55	$218.50
Purchase #3	$56.60	5.365%	$59.6366	$59.64	$59.65	$59.60
Purchase #4	$218.80	13.806%	$249.0075	$249.01	$249.00	$249.00
Purchase #5	$198.27	10.434%	$218.9575	$218.96	$218.95	$219.00
Purchase #6	$249.39	9.649%	$273.4536	$273.45	$273.45	$273.50
Purchase #7	$211.43	5.390%	$222.8261	$222.83	$222.85	$222.80
7 purchase totals =	$1,289.45		$1,408.2109	$1,408.22	$1,408.25	$1,408.20