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	$68.47	13.110%	$77.4464	$77.45	$77.45	$77.40
Purchase #2	$209.53	10.451%	$231.428	$231.43	$231.45	$231.40
Purchase #3	$66.55	6.341%	$70.7699	$70.77	$70.75	$70.80
Purchase #4	$172.88	10.400%	$190.8595	$190.86	$190.85	$190.90
Purchase #5	$42.47	11.682%	$47.4313	$47.43	$47.45	$47.40
Purchase #6	$101.60	11.210%	$112.9894	$112.99	$113.00	$113.00
Purchase #7	$40.85	10.728%	$45.2324	$45.23	$45.25	$45.20
7 purchase totals =	$702.35		$776.1569	$776.16	$776.20	$776.10