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	$161.27	9.688%	$176.8938	$176.89	$176.90	$176.90
Purchase #2	$17.29	6.426%	$18.4011	$18.40	$18.40	$18.40
Purchase #3	$134.36	10.639%	$148.6546	$148.65	$148.65	$148.70
Purchase #4	$164.35	5.474%	$173.3465	$173.35	$173.35	$173.30
Purchase #5	$105.82	7.633%	$113.8972	$113.90	$113.90	$113.90
Purchase #6	$220.45	8.413%	$238.9965	$239.00	$239.00	$239.00
Purchase #7	$116.31	13.427%	$131.9269	$131.93	$131.95	$131.90
7 purchase totals =	$919.85		$1,002.1166	$1,002.12	$1,002.15	$1,002.10