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	$38.45	4.642%	$40.2348	$40.23	$40.25	$40.20
Purchase #2	$138.81	3.766%	$144.0376	$144.04	$144.05	$144.00
Purchase #3	$213.79	11.376%	$238.1108	$238.11	$238.10	$238.10
Purchase #4	$249.65	3.796%	$259.1267	$259.13	$259.15	$259.10
Purchase #5	$127.52	11.336%	$141.9757	$141.98	$142.00	$142.00
Purchase #6	$123.27	13.103%	$139.4221	$139.42	$139.40	$139.40
Purchase #7	$231.30	7.196%	$247.9443	$247.94	$247.95	$247.90
7 purchase totals =	$1,122.79		$1,210.8520	$1,210.85	$1,210.90	$1,210.70