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	$127.29	5.612%	$134.4335	$134.43	$134.45	$134.40
Purchase #2	$54.75	3.356%	$56.5874	$56.59	$56.60	$56.60
Purchase #3	$77.59	9.436%	$84.9114	$84.91	$84.90	$84.90
Purchase #4	$132.37	5.112%	$139.1368	$139.14	$139.15	$139.10
Purchase #5	$240.64	4.859%	$252.3327	$252.33	$252.35	$252.30
Purchase #6	$123.59	4.369%	$128.9896	$128.99	$129.00	$129.00
Purchase #7	$145.59	3.152%	$150.179	$150.18	$150.20	$150.20
7 purchase totals =	$901.82		$946.5704	$946.57	$946.65	$946.50