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	$48.78	10.526%	$53.9146	$53.91	$53.90	$53.90
Purchase #2	$173.61	9.535%	$190.1637	$190.16	$190.15	$190.20
Purchase #3	$158.58	9.540%	$173.7085	$173.71	$173.70	$173.70
Purchase #4	$54.40	5.132%	$57.1918	$57.19	$57.20	$57.20
Purchase #5	$224.45	7.141%	$240.478	$240.48	$240.50	$240.50
Purchase #6	$119.41	6.427%	$127.0845	$127.08	$127.10	$127.10
Purchase #7	$250.78	13.674%	$285.0717	$285.07	$285.05	$285.10
7 purchase totals =	$1,030.01		$1,127.6128	$1,127.60	$1,127.60	$1,127.70