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	$244.82	5.161%	$257.4552	$257.46	$257.45	$257.50
Purchase #2	$229.92	10.741%	$254.6157	$254.62	$254.60	$254.60
Purchase #3	$72.83	13.208%	$82.4494	$82.45	$82.45	$82.40
Purchase #4	$155.72	11.618%	$173.8115	$173.81	$173.80	$173.80
Purchase #5	$236.28	6.420%	$251.4492	$251.45	$251.45	$251.40
Purchase #6	$99.43	6.142%	$105.537	$105.54	$105.55	$105.50
Purchase #7	$52.32	7.412%	$56.198	$56.20	$56.20	$56.20
7 purchase totals =	$1,091.32		$1,181.5160	$1,181.53	$1,181.50	$1,181.40