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	$110.96	11.551%	$123.777	$123.78	$123.80	$123.80
Purchase #2	$210.54	8.628%	$228.7054	$228.71	$228.70	$228.70
Purchase #3	$106.45	9.249%	$116.2956	$116.30	$116.30	$116.30
Purchase #4	$56.59	8.701%	$61.5139	$61.51	$61.50	$61.50
Purchase #5	$232.32	11.451%	$258.923	$258.92	$258.90	$258.90
Purchase #6	$234.42	4.234%	$244.3453	$244.35	$244.35	$244.30
Purchase #7	$49.52	9.703%	$54.3249	$54.32	$54.30	$54.30
7 purchase totals =	$1,000.80		$1,087.8851	$1,087.89	$1,087.85	$1,087.80