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	$235.72	8.311%	$255.3107	$255.31	$255.30	$255.30
Purchase #2	$162.81	10.210%	$179.4329	$179.43	$179.45	$179.40
Purchase #3	$186.62	12.309%	$209.5911	$209.59	$209.60	$209.60
Purchase #4	$65.92	9.147%	$71.9497	$71.95	$71.95	$71.90
Purchase #5	$140.94	10.670%	$155.9783	$155.98	$156.00	$156.00
Purchase #6	$61.88	5.854%	$65.5025	$65.50	$65.50	$65.50
Purchase #7	$27.73	6.580%	$29.5546	$29.55	$29.55	$29.60
7 purchase totals =	$881.62		$967.3198	$967.31	$967.35	$967.30