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	$153.28	8.522%	$166.3425	$166.34	$166.35	$166.30
Purchase #2	$123.35	5.460%	$130.0849	$130.08	$130.10	$130.10
Purchase #3	$250.77	11.398%	$279.3528	$279.35	$279.35	$279.40
Purchase #4	$240.96	4.813%	$252.5574	$252.56	$252.55	$252.60
Purchase #5	$127.40	4.328%	$132.9139	$132.91	$132.90	$132.90
Purchase #6	$212.89	3.154%	$219.6046	$219.60	$219.60	$219.60
Purchase #7	$98.33	13.789%	$111.8887	$111.89	$111.90	$111.90
7 purchase totals =	$1,206.98		$1,292.7448	$1,292.73	$1,292.75	$1,292.80