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	$167.77	10.205%	$184.8909	$184.89	$184.90	$184.90
Purchase #2	$157.50	12.276%	$176.8347	$176.83	$176.85	$176.80
Purchase #3	$229.79	13.476%	$260.7565	$260.76	$260.75	$260.80
Purchase #4	$144.76	8.324%	$156.8098	$156.81	$156.80	$156.80
Purchase #5	$102.90	3.425%	$106.4243	$106.42	$106.40	$106.40
Purchase #6	$146.42	12.691%	$165.0022	$165.00	$165.00	$165.00
Purchase #7	$119.81	6.325%	$127.388	$127.39	$127.40	$127.40
7 purchase totals =	$1,068.95		$1,178.1064	$1,178.10	$1,178.10	$1,178.10