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	$56.64	13.179%	$64.1046	$64.10	$64.10	$64.10
Purchase #2	$65.86	10.169%	$72.5573	$72.56	$72.55	$72.60
Purchase #3	$193.28	9.389%	$211.4271	$211.43	$211.45	$211.40
Purchase #4	$104.35	12.434%	$117.3249	$117.32	$117.30	$117.30
Purchase #5	$68.29	11.182%	$75.9262	$75.93	$75.95	$75.90
Purchase #6	$188.35	12.426%	$211.7544	$211.75	$211.75	$211.80
Purchase #7	$84.73	6.714%	$90.4188	$90.42	$90.40	$90.40
7 purchase totals =	$761.50		$843.5133	$843.51	$843.50	$843.50