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	$26.35	13.163%	$29.8185	$29.82	$29.80	$29.80
Purchase #2	$120.76	6.198%	$128.2447	$128.24	$128.25	$128.20
Purchase #3	$136.63	6.565%	$145.5998	$145.60	$145.60	$145.60
Purchase #4	$153.57	13.712%	$174.6275	$174.63	$174.65	$174.60
Purchase #5	$93.80	6.782%	$100.1615	$100.16	$100.15	$100.20
Purchase #6	$162.89	6.279%	$173.1179	$173.12	$173.10	$173.10
Purchase #7	$51.87	4.342%	$54.1222	$54.12	$54.10	$54.10
7 purchase totals =	$745.87		$805.6921	$805.69	$805.65	$805.60