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	$146.72	6.643%	$156.4666	$156.47	$156.45	$156.50
Purchase #2	$74.55	10.129%	$82.1012	$82.10	$82.10	$82.10
Purchase #3	$33.89	13.628%	$38.5085	$38.51	$38.50	$38.50
Purchase #4	$62.35	9.658%	$68.3718	$68.37	$68.35	$68.40
Purchase #5	$151.46	12.122%	$169.82	$169.82	$169.80	$169.80
Purchase #6	$24.75	4.274%	$25.8078	$25.81	$25.80	$25.80
Purchase #7	$210.77	7.795%	$227.1995	$227.20	$227.20	$227.20
7 purchase totals =	$704.49		$768.2754	$768.28	$768.20	$768.30