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	$38.34	3.483%	$39.6754	$39.68	$39.70	$39.70
Purchase #2	$85.33	4.384%	$89.0709	$89.07	$89.05	$89.10
Purchase #3	$44.34	9.438%	$48.5248	$48.52	$48.50	$48.50
Purchase #4	$173.30	12.279%	$194.5795	$194.58	$194.60	$194.60
Purchase #5	$204.26	6.849%	$218.2498	$218.25	$218.25	$218.20
Purchase #6	$69.95	3.853%	$72.6452	$72.65	$72.65	$72.60
Purchase #7	$170.72	6.455%	$181.74	$181.74	$181.75	$181.70
7 purchase totals =	$786.24		$844.4856	$844.49	$844.50	$844.40