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	$19.33	4.770%	$20.252	$20.25	$20.25	$20.30
Purchase #2	$138.32	13.676%	$157.2366	$157.24	$157.25	$157.20
Purchase #3	$23.52	3.718%	$24.3945	$24.39	$24.40	$24.40
Purchase #4	$40.74	4.598%	$42.6132	$42.61	$42.60	$42.60
Purchase #5	$122.29	3.866%	$127.0177	$127.02	$127.00	$127.00
Purchase #6	$219.50	10.763%	$243.1248	$243.12	$243.10	$243.10
Purchase #7	$180.73	13.787%	$205.6472	$205.65	$205.65	$205.60
7 purchase totals =	$744.43		$820.2860	$820.28	$820.25	$820.20