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	$46.41	6.592%	$49.4693	$49.47	$49.45	$49.50
Purchase #2	$129.81	9.211%	$141.7668	$141.77	$141.75	$141.80
Purchase #3	$186.63	10.179%	$205.6271	$205.63	$205.65	$205.60
Purchase #4	$40.49	5.261%	$42.6202	$42.62	$42.60	$42.60
Purchase #5	$40.27	4.730%	$42.1748	$42.17	$42.15	$42.20
Purchase #6	$71.40	9.223%	$77.9852	$77.99	$78.00	$78.00
Purchase #7	$133.79	8.335%	$144.9414	$144.94	$144.95	$144.90
7 purchase totals =	$648.80		$704.5848	$704.59	$704.55	$704.60