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	$113.66	12.474%	$127.8379	$127.84	$127.85	$127.80
Purchase #2	$40.32	12.529%	$45.3717	$45.37	$45.35	$45.40
Purchase #3	$221.61	5.214%	$233.1647	$233.16	$233.15	$233.20
Purchase #4	$246.86	4.433%	$257.8033	$257.80	$257.80	$257.80
Purchase #5	$54.56	3.365%	$56.3959	$56.40	$56.40	$56.40
Purchase #6	$65.25	7.394%	$70.0746	$70.07	$70.05	$70.10
Purchase #7	$201.34	13.369%	$228.2571	$228.26	$228.25	$228.30
7 purchase totals =	$943.60		$1,018.9052	$1,018.90	$1,018.85	$1,019.00