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	$133.71	13.338%	$151.5442	$151.54	$151.55	$151.50
Purchase #2	$215.85	11.435%	$240.5324	$240.53	$240.55	$240.50
Purchase #3	$97.95	11.871%	$109.5776	$109.58	$109.60	$109.60
Purchase #4	$214.67	7.783%	$231.3778	$231.38	$231.40	$231.40
Purchase #5	$63.32	8.460%	$68.6769	$68.68	$68.70	$68.70
Purchase #6	$32.53	7.584%	$34.9971	$35.00	$35.00	$35.00
Purchase #7	$88.29	12.411%	$99.2477	$99.25	$99.25	$99.20
7 purchase totals =	$846.32		$935.9537	$935.96	$936.05	$935.90