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	$147.55	7.492%	$158.6044	$158.60	$158.60	$158.60
Purchase #2	$155.70	3.149%	$160.603	$160.60	$160.60	$160.60
Purchase #3	$195.77	11.751%	$218.7749	$218.77	$218.75	$218.80
Purchase #4	$146.83	12.291%	$164.8769	$164.88	$164.90	$164.90
Purchase #5	$15.81	13.135%	$17.8866	$17.89	$17.90	$17.90
Purchase #6	$89.37	12.756%	$100.77	$100.77	$100.75	$100.80
Purchase #7	$65.77	9.730%	$72.1694	$72.17	$72.15	$72.20
7 purchase totals =	$816.80		$893.6852	$893.68	$893.65	$893.80