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	$205.31	12.139%	$230.2326	$230.23	$230.25	$230.20
Purchase #2	$218.49	4.859%	$229.1064	$229.11	$229.10	$229.10
Purchase #3	$88.59	12.161%	$99.3634	$99.36	$99.35	$99.40
Purchase #4	$74.47	11.671%	$83.1614	$83.16	$83.15	$83.20
Purchase #5	$69.34	6.126%	$73.5878	$73.59	$73.60	$73.60
Purchase #6	$45.39	10.418%	$50.1187	$50.12	$50.10	$50.10
Purchase #7	$76.66	5.510%	$80.884	$80.88	$80.90	$80.90
7 purchase totals =	$778.25		$846.4543	$846.45	$846.45	$846.50