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	$16.56	8.411%	$17.9529	$17.95	$17.95	$18.00
Purchase #2	$78.60	5.799%	$83.158	$83.16	$83.15	$83.20
Purchase #3	$116.92	10.661%	$129.3848	$129.38	$129.40	$129.40
Purchase #4	$173.65	8.341%	$188.1341	$188.13	$188.15	$188.10
Purchase #5	$183.33	7.357%	$196.8176	$196.82	$196.80	$196.80
Purchase #6	$75.45	3.500%	$78.0908	$78.09	$78.10	$78.10
Purchase #7	$112.71	3.861%	$117.0617	$117.06	$117.05	$117.10
7 purchase totals =	$757.22		$810.5999	$810.59	$810.60	$810.70