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	$179.72	10.411%	$198.4306	$198.43	$198.45	$198.40
Purchase #2	$227.63	8.632%	$247.279	$247.28	$247.30	$247.30
Purchase #3	$78.68	4.694%	$82.3732	$82.37	$82.35	$82.40
Purchase #4	$16.25	7.522%	$17.4723	$17.47	$17.45	$17.50
Purchase #5	$70.88	10.873%	$78.5868	$78.59	$78.60	$78.60
Purchase #6	$53.39	7.255%	$57.2634	$57.26	$57.25	$57.30
Purchase #7	$127.43	9.501%	$139.5371	$139.54	$139.55	$139.50
7 purchase totals =	$753.98		$820.9424	$820.94	$820.95	$821.00