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	$150.30	6.830%	$160.5655	$160.57	$160.55	$160.60
Purchase #2	$174.29	13.746%	$198.2479	$198.25	$198.25	$198.20
Purchase #3	$101.62	9.841%	$111.6204	$111.62	$111.60	$111.60
Purchase #4	$90.93	10.847%	$100.7932	$100.79	$100.80	$100.80
Purchase #5	$60.78	3.320%	$62.7979	$62.80	$62.80	$62.80
Purchase #6	$30.81	8.161%	$33.3244	$33.32	$33.30	$33.30
Purchase #7	$227.27	12.350%	$255.3378	$255.34	$255.35	$255.30
7 purchase totals =	$836.00		$922.6871	$922.69	$922.65	$922.60