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	$138.90	3.694%	$144.031	$144.03	$144.05	$144.00
Purchase #2	$151.64	9.119%	$165.4681	$165.47	$165.45	$165.50
Purchase #3	$175.81	4.390%	$183.5281	$183.53	$183.55	$183.50
Purchase #4	$53.45	6.725%	$57.0445	$57.04	$57.05	$57.00
Purchase #5	$140.35	3.477%	$145.23	$145.23	$145.25	$145.20
Purchase #6	$215.85	10.618%	$238.769	$238.77	$238.75	$238.80
Purchase #7	$49.55	12.502%	$55.7447	$55.74	$55.75	$55.70
7 purchase totals =	$925.55		$989.8154	$989.81	$989.85	$989.70