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	$249.44	10.461%	$275.5339	$275.53	$275.55	$275.50
Purchase #2	$164.80	12.458%	$185.3308	$185.33	$185.35	$185.30
Purchase #3	$230.63	8.635%	$250.5449	$250.54	$250.55	$250.50
Purchase #4	$100.93	4.501%	$105.4729	$105.47	$105.45	$105.50
Purchase #5	$217.54	3.102%	$224.2881	$224.29	$224.30	$224.30
Purchase #6	$244.40	10.224%	$269.3875	$269.39	$269.40	$269.40
Purchase #7	$36.64	5.465%	$38.6424	$38.64	$38.65	$38.60
7 purchase totals =	$1,244.38		$1,349.2005	$1,349.19	$1,349.25	$1,349.10