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	$96.59	8.383%	$104.6871	$104.69	$104.70	$104.70
Purchase #2	$182.47	4.541%	$190.756	$190.76	$190.75	$190.80
Purchase #3	$61.59	3.256%	$63.5954	$63.60	$63.60	$63.60
Purchase #4	$231.63	5.544%	$244.4716	$244.47	$244.45	$244.50
Purchase #5	$37.47	7.240%	$40.1828	$40.18	$40.20	$40.20
Purchase #6	$135.95	4.836%	$142.5245	$142.52	$142.50	$142.50
Purchase #7	$27.81	5.333%	$29.2931	$29.29	$29.30	$29.30
7 purchase totals =	$773.51		$815.5105	$815.51	$815.50	$815.60