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	$234.38	8.154%	$253.4913	$253.49	$253.50	$253.50
Purchase #2	$99.55	12.536%	$112.0296	$112.03	$112.05	$112.00
Purchase #3	$237.71	6.853%	$254.0003	$254.00	$254.00	$254.00
Purchase #4	$72.42	6.822%	$77.3605	$77.36	$77.35	$77.40
Purchase #5	$169.46	9.646%	$185.8061	$185.81	$185.80	$185.80
Purchase #6	$103.76	13.141%	$117.3951	$117.40	$117.40	$117.40
Purchase #7	$41.82	11.200%	$46.5038	$46.50	$46.50	$46.50
7 purchase totals =	$959.10		$1,046.5867	$1,046.59	$1,046.60	$1,046.60