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	$234.56	9.534%	$256.923	$256.92	$256.90	$256.90
Purchase #2	$186.80	12.734%	$210.5871	$210.59	$210.60	$210.60
Purchase #3	$157.78	9.113%	$172.1585	$172.16	$172.15	$172.20
Purchase #4	$52.50	6.108%	$55.7067	$55.71	$55.70	$55.70
Purchase #5	$5.74	7.125%	$6.149	$6.15	$6.15	$6.10
Purchase #6	$124.91	4.158%	$130.1038	$130.10	$130.10	$130.10
Purchase #7	$220.89	7.607%	$237.6931	$237.69	$237.70	$237.70
7 purchase totals =	$983.18		$1,069.3212	$1,069.32	$1,069.30	$1,069.30