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	$241.46	5.674%	$255.1604	$255.16	$255.15	$255.20
Purchase #2	$101.37	6.364%	$107.8212	$107.82	$107.80	$107.80
Purchase #3	$77.59	11.197%	$86.2778	$86.28	$86.30	$86.30
Purchase #4	$172.66	8.492%	$187.3223	$187.32	$187.30	$187.30
Purchase #5	$103.91	10.399%	$114.7156	$114.72	$114.70	$114.70
Purchase #6	$126.41	12.120%	$141.7309	$141.73	$141.75	$141.70
Purchase #7	$101.53	10.728%	$112.4221	$112.42	$112.40	$112.40
7 purchase totals =	$924.93		$1,005.4503	$1,005.45	$1,005.40	$1,005.40