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	$102.37	6.785%	$109.3158	$109.32	$109.30	$109.30
Purchase #2	$204.31	7.852%	$220.3524	$220.35	$220.35	$220.40
Purchase #3	$241.88	13.401%	$274.2943	$274.29	$274.30	$274.30
Purchase #4	$127.84	13.571%	$145.1892	$145.19	$145.20	$145.20
Purchase #5	$227.43	3.233%	$234.7828	$234.78	$234.80	$234.80
Purchase #6	$105.67	10.458%	$116.721	$116.72	$116.70	$116.70
Purchase #7	$62.27	5.606%	$65.7609	$65.76	$65.75	$65.80
7 purchase totals =	$1,071.77		$1,166.4164	$1,166.41	$1,166.40	$1,166.50