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	$96.86	3.809%	$100.5494	$100.55	$100.55	$100.50
Purchase #2	$237.69	9.597%	$260.5011	$260.50	$260.50	$260.50
Purchase #3	$187.41	13.675%	$213.0383	$213.04	$213.05	$213.00
Purchase #4	$200.28	11.586%	$223.4844	$223.48	$223.50	$223.50
Purchase #5	$140.51	13.134%	$158.9646	$158.96	$158.95	$159.00
Purchase #6	$34.72	4.161%	$36.1647	$36.16	$36.15	$36.20
Purchase #7	$220.60	4.743%	$231.0631	$231.06	$231.05	$231.10
7 purchase totals =	$1,118.07		$1,223.7656	$1,223.75	$1,223.75	$1,223.80