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	$36.51	6.633%	$38.9317	$38.93	$38.95	$38.90
Purchase #2	$117.44	5.502%	$123.9015	$123.90	$123.90	$123.90
Purchase #3	$148.51	9.558%	$162.7046	$162.70	$162.70	$162.70
Purchase #4	$56.37	9.783%	$61.8847	$61.88	$61.90	$61.90
Purchase #5	$221.39	4.135%	$230.5445	$230.54	$230.55	$230.50
Purchase #6	$197.45	8.320%	$213.8778	$213.88	$213.90	$213.90
Purchase #7	$63.69	6.280%	$67.6897	$67.69	$67.70	$67.70
7 purchase totals =	$841.36		$899.5345	$899.52	$899.60	$899.50