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	$234.67	9.309%	$256.5154	$256.52	$256.50	$256.50
Purchase #2	$182.30	3.744%	$189.1253	$189.13	$189.15	$189.10
Purchase #3	$226.30	5.522%	$238.7963	$238.80	$238.80	$238.80
Purchase #4	$74.46	11.331%	$82.8971	$82.90	$82.90	$82.90
Purchase #5	$165.82	13.564%	$188.3118	$188.31	$188.30	$188.30
Purchase #6	$126.68	9.240%	$138.3852	$138.39	$138.40	$138.40
Purchase #7	$237.59	4.136%	$247.4167	$247.42	$247.40	$247.40
7 purchase totals =	$1,247.82		$1,341.4478	$1,341.47	$1,341.45	$1,341.40