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	$49.62	11.447%	$55.3	$55.30	$55.30	$55.30
Purchase #2	$182.67	5.731%	$193.1388	$193.14	$193.15	$193.10
Purchase #3	$174.74	3.416%	$180.7091	$180.71	$180.70	$180.70
Purchase #4	$50.76	9.727%	$55.6974	$55.70	$55.70	$55.70
Purchase #5	$119.74	6.458%	$127.4728	$127.47	$127.45	$127.50
Purchase #6	$20.86	3.619%	$21.6149	$21.61	$21.60	$21.60
Purchase #7	$30.83	6.137%	$32.722	$32.72	$32.70	$32.70
7 purchase totals =	$629.22		$666.6550	$666.65	$666.60	$666.60