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	$153.88	7.847%	$165.955	$165.96	$165.95	$166.00
Purchase #2	$133.55	10.855%	$148.0469	$148.05	$148.05	$148.00
Purchase #3	$79.89	8.426%	$86.6215	$86.62	$86.60	$86.60
Purchase #4	$9.86	4.391%	$10.293	$10.29	$10.30	$10.30
Purchase #5	$117.56	13.859%	$133.8526	$133.85	$133.85	$133.90
Purchase #6	$139.94	9.181%	$152.7879	$152.79	$152.80	$152.80
Purchase #7	$105.84	5.402%	$111.5575	$111.56	$111.55	$111.60
7 purchase totals =	$740.52		$809.1144	$809.12	$809.10	$809.20