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	$40.67	4.169%	$42.3655	$42.37	$42.35	$42.40
Purchase #2	$37.54	9.114%	$40.9614	$40.96	$40.95	$41.00
Purchase #3	$172.67	10.469%	$190.7468	$190.75	$190.75	$190.70
Purchase #4	$111.45	13.533%	$126.5325	$126.53	$126.55	$126.50
Purchase #5	$61.54	8.613%	$66.8404	$66.84	$66.85	$66.80
Purchase #6	$219.41	4.538%	$229.3668	$229.37	$229.35	$229.40
Purchase #7	$112.57	5.402%	$118.651	$118.65	$118.65	$118.70
7 purchase totals =	$755.85		$815.4644	$815.47	$815.45	$815.50