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	$14.33	8.437%	$15.539	$15.54	$15.55	$15.50
Purchase #2	$139.63	13.530%	$158.5219	$158.52	$158.50	$158.50
Purchase #3	$160.82	5.379%	$169.4705	$169.47	$169.45	$169.50
Purchase #4	$91.75	8.834%	$99.8552	$99.86	$99.85	$99.90
Purchase #5	$193.93	12.117%	$217.4285	$217.43	$217.45	$217.40
Purchase #6	$121.44	9.636%	$133.142	$133.14	$133.15	$133.10
Purchase #7	$33.65	8.843%	$36.6257	$36.63	$36.65	$36.60
7 purchase totals =	$755.55		$830.5828	$830.59	$830.60	$830.50