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	$237.71	7.209%	$254.8465	$254.85	$254.85	$254.80
Purchase #2	$143.44	6.415%	$152.6417	$152.64	$152.65	$152.60
Purchase #3	$175.51	8.382%	$190.2212	$190.22	$190.20	$190.20
Purchase #4	$119.71	10.509%	$132.2903	$132.29	$132.30	$132.30
Purchase #5	$162.69	10.778%	$180.2247	$180.22	$180.20	$180.20
Purchase #6	$244.90	12.652%	$275.8847	$275.88	$275.90	$275.90
Purchase #7	$101.43	13.326%	$114.9466	$114.95	$114.95	$114.90
7 purchase totals =	$1,185.39		$1,301.0557	$1,301.05	$1,301.05	$1,300.90