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	$38.60	5.103%	$40.5698	$40.57	$40.55	$40.60
Purchase #2	$34.28	5.821%	$36.2754	$36.28	$36.30	$36.30
Purchase #3	$117.90	4.615%	$123.3411	$123.34	$123.35	$123.30
Purchase #4	$73.37	12.271%	$82.3732	$82.37	$82.35	$82.40
Purchase #5	$50.52	7.178%	$54.1463	$54.15	$54.15	$54.10
Purchase #6	$217.34	6.638%	$231.767	$231.77	$231.75	$231.80
Purchase #7	$216.65	4.285%	$225.9335	$225.93	$225.95	$225.90
7 purchase totals =	$748.66		$794.4063	$794.41	$794.40	$794.40