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	$13.60	11.574%	$15.1741	$15.17	$15.15	$15.20
Purchase #2	$111.70	10.420%	$123.3391	$123.34	$123.35	$123.30
Purchase #3	$223.73	6.585%	$238.4626	$238.46	$238.45	$238.50
Purchase #4	$28.73	4.343%	$29.9777	$29.98	$30.00	$30.00
Purchase #5	$15.99	10.215%	$17.6234	$17.62	$17.60	$17.60
Purchase #6	$62.31	7.765%	$67.1484	$67.15	$67.15	$67.10
Purchase #7	$131.33	11.150%	$145.9733	$145.97	$145.95	$146.00
7 purchase totals =	$587.39		$637.6986	$637.69	$637.65	$637.70