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	$97.55	6.848%	$104.2302	$104.23	$104.25	$104.20
Purchase #2	$30.88	7.590%	$33.2238	$33.22	$33.20	$33.20
Purchase #3	$13.79	12.351%	$15.4932	$15.49	$15.50	$15.50
Purchase #4	$87.94	5.588%	$92.8541	$92.85	$92.85	$92.90
Purchase #5	$33.69	7.154%	$36.1002	$36.10	$36.10	$36.10
Purchase #6	$103.43	7.546%	$111.2348	$111.23	$111.25	$111.20
Purchase #7	$178.52	12.410%	$200.6743	$200.67	$200.65	$200.70
7 purchase totals =	$545.80		$593.8106	$593.79	$593.80	$593.80