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	$101.88	13.361%	$115.4922	$115.49	$115.50	$115.50
Purchase #2	$48.40	12.462%	$54.4316	$54.43	$54.45	$54.40
Purchase #3	$110.40	12.548%	$124.253	$124.25	$124.25	$124.30
Purchase #4	$25.82	5.551%	$27.2533	$27.25	$27.25	$27.30
Purchase #5	$131.46	4.360%	$137.1917	$137.19	$137.20	$137.20
Purchase #6	$136.60	4.794%	$143.1486	$143.15	$143.15	$143.10
Purchase #7	$39.94	11.366%	$44.4796	$44.48	$44.50	$44.50
7 purchase totals =	$594.50		$646.2500	$646.24	$646.30	$646.30