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	$71.30	8.574%	$77.4133	$77.41	$77.40	$77.40
Purchase #2	$103.89	8.791%	$113.023	$113.02	$113.00	$113.00
Purchase #3	$79.91	12.794%	$90.1337	$90.13	$90.15	$90.10
Purchase #4	$34.70	9.542%	$38.0111	$38.01	$38.00	$38.00
Purchase #5	$148.79	6.492%	$158.4494	$158.45	$158.45	$158.40
Purchase #6	$158.65	6.772%	$169.3938	$169.39	$169.40	$169.40
Purchase #7	$247.27	6.320%	$262.8975	$262.90	$262.90	$262.90
7 purchase totals =	$844.51		$909.3218	$909.31	$909.30	$909.20