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	$233.71	9.204%	$255.2207	$255.22	$255.20	$255.20
Purchase #2	$233.92	13.280%	$264.9846	$264.98	$265.00	$265.00
Purchase #3	$144.65	13.312%	$163.9058	$163.91	$163.90	$163.90
Purchase #4	$111.32	13.534%	$126.386	$126.39	$126.40	$126.40
Purchase #5	$172.68	13.782%	$196.4788	$196.48	$196.50	$196.50
Purchase #6	$136.32	4.153%	$141.9814	$141.98	$142.00	$142.00
Purchase #7	$221.29	4.367%	$230.9537	$230.95	$230.95	$231.00
7 purchase totals =	$1,253.89		$1,379.9110	$1,379.91	$1,379.95	$1,380.00