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	$152.45	13.514%	$173.0521	$173.05	$173.05	$173.10
Purchase #2	$67.89	4.445%	$70.9077	$70.91	$70.90	$70.90
Purchase #3	$112.79	4.504%	$117.8701	$117.87	$117.85	$117.90
Purchase #4	$250.31	11.847%	$279.9642	$279.96	$279.95	$280.00
Purchase #5	$6.81	5.652%	$7.1949	$7.19	$7.20	$7.20
Purchase #6	$28.53	3.152%	$29.4293	$29.43	$29.45	$29.40
Purchase #7	$99.69	11.442%	$111.0965	$111.10	$111.10	$111.10
7 purchase totals =	$718.47		$789.5148	$789.51	$789.50	$789.60