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	$242.36	9.810%	$266.1355	$266.14	$266.15	$266.10
Purchase #2	$182.87	3.728%	$189.6874	$189.69	$189.70	$189.70
Purchase #3	$141.52	9.319%	$154.7082	$154.71	$154.70	$154.70
Purchase #4	$88.41	13.367%	$100.2278	$100.23	$100.25	$100.20
Purchase #5	$70.30	11.493%	$78.3796	$78.38	$78.40	$78.40
Purchase #6	$114.29	3.297%	$118.0581	$118.06	$118.05	$118.10
Purchase #7	$246.79	7.439%	$265.1487	$265.15	$265.15	$265.10
7 purchase totals =	$1,086.54		$1,172.3453	$1,172.36	$1,172.40	$1,172.30