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	$38.25	6.653%	$40.7948	$40.79	$40.80	$40.80
Purchase #2	$214.53	4.857%	$224.9497	$224.95	$224.95	$224.90
Purchase #3	$74.59	5.445%	$78.6514	$78.65	$78.65	$78.70
Purchase #4	$48.47	11.295%	$53.9447	$53.94	$53.95	$53.90
Purchase #5	$138.47	7.329%	$148.6185	$148.62	$148.60	$148.60
Purchase #6	$179.36	3.566%	$185.756	$185.76	$185.75	$185.80
Purchase #7	$74.53	11.559%	$83.1449	$83.14	$83.15	$83.10
7 purchase totals =	$768.20		$815.8600	$815.85	$815.85	$815.80