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	$246.44	3.579%	$255.2601	$255.26	$255.25	$255.30
Purchase #2	$244.96	6.472%	$260.8138	$260.81	$260.80	$260.80
Purchase #3	$169.56	13.622%	$192.6575	$192.66	$192.65	$192.70
Purchase #4	$43.67	3.264%	$45.0954	$45.10	$45.10	$45.10
Purchase #5	$152.95	9.300%	$167.1744	$167.17	$167.15	$167.20
Purchase #6	$42.39	10.562%	$46.8672	$46.87	$46.85	$46.90
Purchase #7	$186.51	13.169%	$211.0715	$211.07	$211.05	$211.10
7 purchase totals =	$1,086.48		$1,178.9399	$1,178.94	$1,178.85	$1,179.10