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	$133.76	13.553%	$151.8885	$151.89	$151.90	$151.90
Purchase #2	$226.59	10.541%	$250.4749	$250.47	$250.45	$250.50
Purchase #3	$247.29	11.178%	$274.9321	$274.93	$274.95	$274.90
Purchase #4	$100.99	7.513%	$108.5774	$108.58	$108.60	$108.60
Purchase #5	$142.51	12.450%	$160.2525	$160.25	$160.25	$160.30
Purchase #6	$238.82	13.246%	$270.4541	$270.45	$270.45	$270.50
Purchase #7	$28.28	13.476%	$32.091	$32.09	$32.10	$32.10
7 purchase totals =	$1,118.24		$1,248.6705	$1,248.66	$1,248.70	$1,248.80