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	$80.99	11.562%	$90.3541	$90.35	$90.35	$90.40
Purchase #2	$52.32	11.405%	$58.2871	$58.29	$58.30	$58.30
Purchase #3	$211.40	10.417%	$233.4215	$233.42	$233.40	$233.40
Purchase #4	$118.44	11.426%	$131.973	$131.97	$131.95	$132.00
Purchase #5	$39.79	8.194%	$43.0504	$43.05	$43.05	$43.10
Purchase #6	$71.31	13.634%	$81.0324	$81.03	$81.05	$81.00
Purchase #7	$141.86	11.652%	$158.3895	$158.39	$158.40	$158.40
7 purchase totals =	$716.11		$796.5080	$796.50	$796.50	$796.60