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	$110.69	11.214%	$123.1028	$123.10	$123.10	$123.10
Purchase #2	$183.80	13.832%	$209.2232	$209.22	$209.20	$209.20
Purchase #3	$55.71	7.247%	$59.7473	$59.75	$59.75	$59.70
Purchase #4	$103.56	7.394%	$111.2172	$111.22	$111.20	$111.20
Purchase #5	$123.41	6.263%	$131.1392	$131.14	$131.15	$131.10
Purchase #6	$53.26	12.744%	$60.0475	$60.05	$60.05	$60.00
Purchase #7	$109.60	10.601%	$121.2187	$121.22	$121.20	$121.20
7 purchase totals =	$740.03		$815.6959	$815.70	$815.65	$815.50