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	$137.92	10.434%	$152.3106	$152.31	$152.30	$152.30
Purchase #2	$152.47	12.733%	$171.884	$171.88	$171.90	$171.90
Purchase #3	$37.99	6.490%	$40.4556	$40.46	$40.45	$40.50
Purchase #4	$99.85	3.198%	$103.0432	$103.04	$103.05	$103.00
Purchase #5	$121.31	13.431%	$137.6031	$137.60	$137.60	$137.60
Purchase #6	$153.39	6.366%	$163.1548	$163.15	$163.15	$163.20
Purchase #7	$96.29	13.868%	$109.6435	$109.64	$109.65	$109.60
7 purchase totals =	$799.22		$878.0948	$878.08	$878.10	$878.10