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	$109.38	3.450%	$113.1536	$113.15	$113.15	$113.20
Purchase #2	$153.91	6.799%	$164.3743	$164.37	$164.35	$164.40
Purchase #3	$76.80	3.676%	$79.6232	$79.62	$79.60	$79.60
Purchase #4	$86.36	7.647%	$92.9639	$92.96	$92.95	$93.00
Purchase #5	$91.97	10.119%	$101.2764	$101.28	$101.30	$101.30
Purchase #6	$20.52	3.128%	$21.1619	$21.16	$21.15	$21.20
Purchase #7	$103.91	7.231%	$111.4237	$111.42	$111.40	$111.40
7 purchase totals =	$642.85		$683.9770	$683.96	$683.90	$684.10