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	$143.57	10.362%	$158.4467	$158.45	$158.45	$158.40
Purchase #2	$72.41	7.156%	$77.5917	$77.59	$77.60	$77.60
Purchase #3	$64.40	10.541%	$71.1884	$71.19	$71.20	$71.20
Purchase #4	$137.66	13.434%	$156.1532	$156.15	$156.15	$156.20
Purchase #5	$164.66	12.671%	$185.5241	$185.52	$185.50	$185.50
Purchase #6	$151.58	7.447%	$162.8682	$162.87	$162.85	$162.90
Purchase #7	$163.81	8.639%	$177.9615	$177.96	$177.95	$178.00
7 purchase totals =	$898.09		$989.7338	$989.73	$989.70	$989.80