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	$164.94	5.426%	$173.8896	$173.89	$173.90	$173.90
Purchase #2	$110.64	4.708%	$115.8489	$115.85	$115.85	$115.80
Purchase #3	$231.74	4.207%	$241.4893	$241.49	$241.50	$241.50
Purchase #4	$85.31	6.397%	$90.7673	$90.77	$90.75	$90.80
Purchase #5	$25.70	5.415%	$27.0917	$27.09	$27.10	$27.10
Purchase #6	$95.88	4.592%	$100.2828	$100.28	$100.30	$100.30
Purchase #7	$75.77	13.591%	$86.0679	$86.07	$86.05	$86.10
7 purchase totals =	$789.98		$835.4375	$835.44	$835.45	$835.50