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	$211.29	9.139%	$230.5998	$230.60	$230.60	$230.60
Purchase #2	$181.74	4.173%	$189.324	$189.32	$189.30	$189.30
Purchase #3	$22.65	7.636%	$24.3796	$24.38	$24.40	$24.40
Purchase #4	$217.59	7.181%	$233.2151	$233.22	$233.20	$233.20
Purchase #5	$6.83	4.286%	$7.1227	$7.12	$7.10	$7.10
Purchase #6	$72.29	8.270%	$78.2684	$78.27	$78.25	$78.30
Purchase #7	$203.98	4.227%	$212.6022	$212.60	$212.60	$212.60
7 purchase totals =	$916.37		$975.5118	$975.51	$975.45	$975.50