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	$101.29	12.758%	$114.2126	$114.21	$114.20	$114.20
Purchase #2	$56.87	10.674%	$62.9403	$62.94	$62.95	$62.90
Purchase #3	$156.58	9.202%	$170.9885	$170.99	$171.00	$171.00
Purchase #4	$229.41	12.225%	$257.4554	$257.46	$257.45	$257.50
Purchase #5	$95.98	4.833%	$100.6187	$100.62	$100.60	$100.60
Purchase #6	$36.82	6.819%	$39.3308	$39.33	$39.35	$39.30
Purchase #7	$127.38	13.469%	$144.5368	$144.54	$144.55	$144.50
7 purchase totals =	$804.33		$890.0831	$890.09	$890.10	$890.00