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	$91.55	8.138%	$99.0003	$99.00	$99.00	$99.00
Purchase #2	$114.65	11.448%	$127.7751	$127.78	$127.80	$127.80
Purchase #3	$17.32	12.874%	$19.5498	$19.55	$19.55	$19.50
Purchase #4	$212.49	12.619%	$239.3041	$239.30	$239.30	$239.30
Purchase #5	$104.26	6.704%	$111.2496	$111.25	$111.25	$111.20
Purchase #6	$58.99	11.679%	$65.8794	$65.88	$65.90	$65.90
Purchase #7	$152.37	9.254%	$166.4703	$166.47	$166.45	$166.50
7 purchase totals =	$751.63		$829.2286	$829.23	$829.25	$829.20