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	$189.34	9.239%	$206.8331	$206.83	$206.85	$206.80
Purchase #2	$100.77	11.860%	$112.7213	$112.72	$112.70	$112.70
Purchase #3	$216.86	5.382%	$228.5314	$228.53	$228.55	$228.50
Purchase #4	$103.68	7.182%	$111.1263	$111.13	$111.15	$111.10
Purchase #5	$82.73	8.665%	$89.8986	$89.90	$89.90	$89.90
Purchase #6	$179.55	11.567%	$200.3185	$200.32	$200.30	$200.30
Purchase #7	$216.29	5.765%	$228.7591	$228.76	$228.75	$228.80
7 purchase totals =	$1,089.22		$1,178.1883	$1,178.19	$1,178.20	$1,178.10