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	$89.68	12.571%	$100.9537	$100.95	$100.95	$101.00
Purchase #2	$132.96	9.229%	$145.2309	$145.23	$145.25	$145.20
Purchase #3	$64.85	10.313%	$71.538	$71.54	$71.55	$71.50
Purchase #4	$219.83	6.855%	$234.8993	$234.90	$234.90	$234.90
Purchase #5	$145.98	11.362%	$162.5662	$162.57	$162.55	$162.60
Purchase #6	$99.50	9.211%	$108.6649	$108.66	$108.65	$108.70
Purchase #7	$48.44	8.541%	$52.5773	$52.58	$52.60	$52.60
7 purchase totals =	$801.24		$876.4303	$876.43	$876.45	$876.50