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	$35.67	9.233%	$38.9634	$38.96	$38.95	$39.00
Purchase #2	$118.76	7.727%	$127.9366	$127.94	$127.95	$127.90
Purchase #3	$151.37	4.700%	$158.4844	$158.48	$158.50	$158.50
Purchase #4	$217.69	3.114%	$224.4689	$224.47	$224.45	$224.50
Purchase #5	$65.78	5.328%	$69.2848	$69.28	$69.30	$69.30
Purchase #6	$54.89	11.393%	$61.1436	$61.14	$61.15	$61.10
Purchase #7	$170.27	9.588%	$186.5955	$186.60	$186.60	$186.60
7 purchase totals =	$814.43		$866.8772	$866.87	$866.90	$866.90