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	$15.93	12.361%	$17.8991	$17.90	$17.90	$17.90
Purchase #2	$78.43	11.325%	$87.3122	$87.31	$87.30	$87.30
Purchase #3	$38.82	7.180%	$41.6073	$41.61	$41.60	$41.60
Purchase #4	$172.29	8.587%	$187.0845	$187.08	$187.10	$187.10
Purchase #5	$29.74	11.740%	$33.2315	$33.23	$33.25	$33.20
Purchase #6	$40.60	9.435%	$44.4306	$44.43	$44.45	$44.40
Purchase #7	$53.71	13.616%	$61.0232	$61.02	$61.00	$61.00
7 purchase totals =	$429.52		$472.5884	$472.58	$472.60	$472.50