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	$238.65	7.261%	$255.9784	$255.98	$256.00	$256.00
Purchase #2	$134.84	13.778%	$153.4183	$153.42	$153.40	$153.40
Purchase #3	$241.59	13.467%	$274.1249	$274.12	$274.10	$274.10
Purchase #4	$71.98	9.461%	$78.79	$78.79	$78.80	$78.80
Purchase #5	$10.69	7.122%	$11.4513	$11.45	$11.45	$11.50
Purchase #6	$86.71	5.553%	$91.525	$91.53	$91.55	$91.50
Purchase #7	$85.44	9.687%	$93.7166	$93.72	$93.70	$93.70
7 purchase totals =	$869.90		$959.0045	$959.01	$959.00	$959.00