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	$161.33	9.274%	$176.2917	$176.29	$176.30	$176.30
Purchase #2	$104.54	6.684%	$111.5275	$111.53	$111.55	$111.50
Purchase #3	$122.83	12.132%	$137.7317	$137.73	$137.75	$137.70
Purchase #4	$151.57	13.860%	$172.5776	$172.58	$172.60	$172.60
Purchase #5	$98.33	7.440%	$105.6458	$105.65	$105.65	$105.60
Purchase #6	$140.90	4.640%	$147.4378	$147.44	$147.45	$147.40
Purchase #7	$73.73	6.495%	$78.5188	$78.52	$78.50	$78.50
7 purchase totals =	$853.23		$929.7309	$929.74	$929.80	$929.60