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	$48.30	10.212%	$53.2324	$53.23	$53.25	$53.20
Purchase #2	$227.55	13.676%	$258.6697	$258.67	$258.65	$258.70
Purchase #3	$107.49	3.668%	$111.4327	$111.43	$111.45	$111.40
Purchase #4	$96.75	5.556%	$102.1254	$102.13	$102.15	$102.10
Purchase #5	$49.76	9.523%	$54.4986	$54.50	$54.50	$54.50
Purchase #6	$225.49	3.365%	$233.0777	$233.08	$233.10	$233.10
Purchase #7	$40.34	11.760%	$45.084	$45.08	$45.10	$45.10
7 purchase totals =	$795.68		$858.1205	$858.12	$858.20	$858.10