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	$183.65	3.172%	$189.4754	$189.48	$189.50	$189.50
Purchase #2	$37.79	4.839%	$39.6187	$39.62	$39.60	$39.60
Purchase #3	$107.98	3.144%	$111.3749	$111.37	$111.35	$111.40
Purchase #4	$119.28	4.461%	$124.6011	$124.60	$124.60	$124.60
Purchase #5	$20.49	5.546%	$21.6264	$21.63	$21.65	$21.60
Purchase #6	$246.31	3.709%	$255.4456	$255.45	$255.45	$255.40
Purchase #7	$5.29	4.324%	$5.5187	$5.52	$5.50	$5.50
7 purchase totals =	$720.79		$747.6608	$747.67	$747.65	$747.60