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	$163.32	12.647%	$183.9751	$183.98	$184.00	$184.00
Purchase #2	$55.95	6.833%	$59.7731	$59.77	$59.75	$59.80
Purchase #3	$174.49	13.728%	$198.444	$198.44	$198.45	$198.40
Purchase #4	$158.45	5.711%	$167.4991	$167.50	$167.50	$167.50
Purchase #5	$222.31	3.623%	$230.3643	$230.36	$230.35	$230.40
Purchase #6	$169.78	9.318%	$185.6001	$185.60	$185.60	$185.60
Purchase #7	$194.60	7.362%	$208.9265	$208.93	$208.95	$208.90
7 purchase totals =	$1,138.90		$1,234.5822	$1,234.58	$1,234.60	$1,234.60