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	$18.78	9.466%	$20.5577	$20.56	$20.55	$20.60
Purchase #2	$18.97	5.723%	$20.0557	$20.06	$20.05	$20.10
Purchase #3	$10.81	3.244%	$11.1607	$11.16	$11.15	$11.20
Purchase #4	$46.40	5.270%	$48.8453	$48.85	$48.85	$48.80
Purchase #5	$106.46	11.673%	$118.8871	$118.89	$118.90	$118.90
Purchase #6	$206.37	11.839%	$230.8021	$230.80	$230.80	$230.80
Purchase #7	$89.74	7.588%	$96.5495	$96.55	$96.55	$96.50
7 purchase totals =	$497.53		$546.8581	$546.87	$546.85	$546.90