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	$28.69	11.380%	$31.9549	$31.95	$31.95	$32.00
Purchase #2	$133.66	10.382%	$147.5366	$147.54	$147.55	$147.50
Purchase #3	$150.93	6.240%	$160.348	$160.35	$160.35	$160.30
Purchase #4	$90.73	11.162%	$100.8573	$100.86	$100.85	$100.90
Purchase #5	$104.80	3.819%	$108.8023	$108.80	$108.80	$108.80
Purchase #6	$112.49	9.599%	$123.2879	$123.29	$123.30	$123.30
Purchase #7	$113.85	7.299%	$122.1599	$122.16	$122.15	$122.20
7 purchase totals =	$735.15		$794.9469	$794.95	$794.95	$795.00