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	$24.43	9.826%	$26.8305	$26.83	$26.85	$26.80
Purchase #2	$125.25	12.433%	$140.8223	$140.82	$140.80	$140.80
Purchase #3	$129.60	11.212%	$144.1308	$144.13	$144.15	$144.10
Purchase #4	$146.39	3.410%	$151.3819	$151.38	$151.40	$151.40
Purchase #5	$210.50	5.137%	$221.3134	$221.31	$221.30	$221.30
Purchase #6	$243.93	7.393%	$261.9637	$261.96	$261.95	$262.00
Purchase #7	$138.67	11.384%	$154.4562	$154.46	$154.45	$154.50
7 purchase totals =	$1,018.77		$1,100.8988	$1,100.89	$1,100.90	$1,100.90