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	$17.36	5.730%	$18.3547	$18.35	$18.35	$18.40
Purchase #2	$250.79	11.762%	$280.2879	$280.29	$280.30	$280.30
Purchase #3	$148.44	5.494%	$156.5953	$156.60	$156.60	$156.60
Purchase #4	$104.84	9.663%	$114.9707	$114.97	$114.95	$115.00
Purchase #5	$147.49	7.309%	$158.27	$158.27	$158.25	$158.30
Purchase #6	$238.42	5.102%	$250.5842	$250.58	$250.60	$250.60
Purchase #7	$25.73	13.103%	$29.1014	$29.10	$29.10	$29.10
7 purchase totals =	$933.07		$1,008.1642	$1,008.16	$1,008.15	$1,008.30