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	$164.96	12.686%	$185.8868	$185.89	$185.90	$185.90
Purchase #2	$147.95	4.768%	$155.0043	$155.00	$155.00	$155.00
Purchase #3	$122.28	7.728%	$131.7298	$131.73	$131.75	$131.70
Purchase #4	$126.26	10.841%	$139.9478	$139.95	$139.95	$139.90
Purchase #5	$90.49	10.307%	$99.8168	$99.82	$99.80	$99.80
Purchase #6	$163.47	5.836%	$173.0101	$173.01	$173.00	$173.00
Purchase #7	$85.74	5.860%	$90.7644	$90.76	$90.75	$90.80
7 purchase totals =	$901.15		$976.1600	$976.16	$976.15	$976.10