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	$249.89	10.245%	$275.4912	$275.49	$275.50	$275.50
Purchase #2	$236.73	7.420%	$254.2954	$254.30	$254.30	$254.30
Purchase #3	$126.34	6.310%	$134.3121	$134.31	$134.30	$134.30
Purchase #4	$233.87	9.852%	$256.9109	$256.91	$256.90	$256.90
Purchase #5	$109.54	5.820%	$115.9152	$115.92	$115.90	$115.90
Purchase #6	$63.74	13.868%	$72.5795	$72.58	$72.60	$72.60
Purchase #7	$164.35	10.677%	$181.8976	$181.90	$181.90	$181.90
7 purchase totals =	$1,184.46		$1,291.4019	$1,291.41	$1,291.40	$1,291.40