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	$90.71	10.826%	$100.5303	$100.53	$100.55	$100.50
Purchase #2	$70.90	10.217%	$78.1439	$78.14	$78.15	$78.10
Purchase #3	$199.94	10.611%	$221.1556	$221.16	$221.15	$221.20
Purchase #4	$215.39	11.239%	$239.5977	$239.60	$239.60	$239.60
Purchase #5	$98.65	6.565%	$105.1264	$105.13	$105.15	$105.10
Purchase #6	$203.83	7.693%	$219.5106	$219.51	$219.50	$219.50
Purchase #7	$33.50	10.191%	$36.914	$36.91	$36.90	$36.90
7 purchase totals =	$912.92		$1,000.9785	$1,000.98	$1,001.00	$1,000.90