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	$91.67	9.646%	$100.5125	$100.51	$100.50	$100.50
Purchase #2	$126.60	11.808%	$141.5489	$141.55	$141.55	$141.50
Purchase #3	$121.34	4.872%	$127.2517	$127.25	$127.25	$127.30
Purchase #4	$123.27	13.116%	$139.4381	$139.44	$139.45	$139.40
Purchase #5	$19.85	4.676%	$20.7782	$20.78	$20.80	$20.80
Purchase #6	$19.51	10.433%	$21.5455	$21.55	$21.55	$21.50
Purchase #7	$133.41	5.357%	$140.5568	$140.56	$140.55	$140.60
7 purchase totals =	$635.65		$691.6317	$691.64	$691.65	$691.60