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	$120.87	5.608%	$127.6484	$127.65	$127.65	$127.60
Purchase #2	$19.81	11.347%	$22.0578	$22.06	$22.05	$22.10
Purchase #3	$167.80	13.702%	$190.792	$190.79	$190.80	$190.80
Purchase #4	$19.27	13.138%	$21.8017	$21.80	$21.80	$21.80
Purchase #5	$69.51	4.581%	$72.6943	$72.69	$72.70	$72.70
Purchase #6	$148.60	11.484%	$165.6652	$165.67	$165.65	$165.70
Purchase #7	$58.80	12.714%	$66.2758	$66.28	$66.30	$66.30
7 purchase totals =	$604.66		$666.9352	$666.94	$666.95	$667.00