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	$179.27	6.379%	$190.7056	$190.71	$190.70	$190.70
Purchase #2	$200.92	10.766%	$222.551	$222.55	$222.55	$222.60
Purchase #3	$246.25	11.527%	$274.6352	$274.64	$274.65	$274.60
Purchase #4	$119.54	7.803%	$128.8677	$128.87	$128.85	$128.90
Purchase #5	$92.87	8.569%	$100.828	$100.83	$100.85	$100.80
Purchase #6	$51.94	5.146%	$54.6128	$54.61	$54.60	$54.60
Purchase #7	$148.36	12.546%	$166.9732	$166.97	$166.95	$167.00
7 purchase totals =	$1,039.15		$1,139.1735	$1,139.18	$1,139.15	$1,139.20