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	$7.72	11.368%	$8.5976	$8.60	$8.60	$8.60
Purchase #2	$225.49	10.621%	$249.4393	$249.44	$249.45	$249.40
Purchase #3	$14.97	3.705%	$15.5246	$15.52	$15.50	$15.50
Purchase #4	$97.72	13.797%	$111.2024	$111.20	$111.20	$111.20
Purchase #5	$45.33	9.445%	$49.6114	$49.61	$49.60	$49.60
Purchase #6	$214.55	12.540%	$241.4546	$241.45	$241.45	$241.50
Purchase #7	$162.78	6.712%	$173.7058	$173.71	$173.70	$173.70
7 purchase totals =	$768.56		$849.5357	$849.53	$849.50	$849.50