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	$89.45	12.403%	$100.5445	$100.54	$100.55	$100.50
Purchase #2	$241.80	10.567%	$267.351	$267.35	$267.35	$267.40
Purchase #3	$248.69	3.232%	$256.7277	$256.73	$256.75	$256.70
Purchase #4	$102.68	11.853%	$114.8507	$114.85	$114.85	$114.90
Purchase #5	$106.56	10.558%	$117.8106	$117.81	$117.80	$117.80
Purchase #6	$117.25	9.303%	$128.1578	$128.16	$128.15	$128.20
Purchase #7	$99.54	11.643%	$111.1294	$111.13	$111.15	$111.10
7 purchase totals =	$1,005.97		$1,096.5717	$1,096.57	$1,096.60	$1,096.60