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	$27.37	6.541%	$29.1603	$29.16	$29.15	$29.20
Purchase #2	$132.94	6.520%	$141.6077	$141.61	$141.60	$141.60
Purchase #3	$12.33	12.194%	$13.8335	$13.83	$13.85	$13.80
Purchase #4	$175.94	9.591%	$192.8144	$192.81	$192.80	$192.80
Purchase #5	$29.51	10.278%	$32.543	$32.54	$32.55	$32.50
Purchase #6	$101.72	9.267%	$111.1464	$111.15	$111.15	$111.10
Purchase #7	$74.44	3.629%	$77.1414	$77.14	$77.15	$77.10
7 purchase totals =	$554.25		$598.2467	$598.24	$598.25	$598.10