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	$26.48	3.840%	$27.4968	$27.50	$27.50	$27.50
Purchase #2	$161.32	5.169%	$169.6586	$169.66	$169.65	$169.70
Purchase #3	$144.57	4.748%	$151.4342	$151.43	$151.45	$151.40
Purchase #4	$145.54	12.798%	$164.1662	$164.17	$164.15	$164.20
Purchase #5	$238.98	3.456%	$247.2391	$247.24	$247.25	$247.20
Purchase #6	$104.68	4.144%	$109.0179	$109.02	$109.00	$109.00
Purchase #7	$107.71	3.804%	$111.8073	$111.81	$111.80	$111.80
7 purchase totals =	$929.28		$980.8201	$980.83	$980.80	$980.80