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	$182.85	3.762%	$189.7288	$189.73	$189.75	$189.70
Purchase #2	$157.93	10.845%	$175.0575	$175.06	$175.05	$175.10
Purchase #3	$86.52	3.235%	$89.3189	$89.32	$89.30	$89.30
Purchase #4	$114.29	6.594%	$121.8263	$121.83	$121.85	$121.80
Purchase #5	$173.85	5.146%	$182.7963	$182.80	$182.80	$182.80
Purchase #6	$86.56	6.689%	$92.35	$92.35	$92.35	$92.40
Purchase #7	$112.49	13.417%	$127.5828	$127.58	$127.60	$127.60
7 purchase totals =	$914.49		$978.6606	$978.67	$978.70	$978.70