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	$119.72	5.670%	$126.5081	$126.51	$126.50	$126.50
Purchase #2	$205.74	13.561%	$233.6404	$233.64	$233.65	$233.60
Purchase #3	$101.72	10.421%	$112.3202	$112.32	$112.30	$112.30
Purchase #4	$10.45	7.399%	$11.2232	$11.22	$11.20	$11.20
Purchase #5	$226.28	10.576%	$250.2114	$250.21	$250.20	$250.20
Purchase #6	$31.88	4.481%	$33.3085	$33.31	$33.30	$33.30
Purchase #7	$57.30	12.449%	$64.4333	$64.43	$64.45	$64.40
7 purchase totals =	$753.09		$831.6451	$831.64	$831.60	$831.50