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	$37.39	7.797%	$40.3053	$40.31	$40.30	$40.30
Purchase #2	$135.60	5.196%	$142.6458	$142.65	$142.65	$142.60
Purchase #3	$214.90	4.149%	$223.8162	$223.82	$223.80	$223.80
Purchase #4	$153.97	3.730%	$159.7131	$159.71	$159.70	$159.70
Purchase #5	$107.74	3.594%	$111.6122	$111.61	$111.60	$111.60
Purchase #6	$63.38	12.287%	$71.1675	$71.17	$71.15	$71.20
Purchase #7	$104.29	12.295%	$117.1125	$117.11	$117.10	$117.10
7 purchase totals =	$817.27		$866.3726	$866.38	$866.30	$866.30