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	$94.34	9.334%	$103.1457	$103.15	$103.15	$103.10
Purchase #2	$239.45	9.646%	$262.5473	$262.55	$262.55	$262.50
Purchase #3	$200.61	12.685%	$226.0574	$226.06	$226.05	$226.10
Purchase #4	$125.39	11.628%	$139.9703	$139.97	$139.95	$140.00
Purchase #5	$18.38	9.587%	$20.1421	$20.14	$20.15	$20.10
Purchase #6	$110.83	11.637%	$123.7273	$123.73	$123.75	$123.70
Purchase #7	$108.85	13.510%	$123.5556	$123.56	$123.55	$123.60
7 purchase totals =	$897.85		$999.1457	$999.16	$999.15	$999.10