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	$248.62	3.211%	$256.6032	$256.60	$256.60	$256.60
Purchase #2	$110.95	10.385%	$122.4722	$122.47	$122.45	$122.50
Purchase #3	$85.51	4.610%	$89.452	$89.45	$89.45	$89.50
Purchase #4	$60.86	10.818%	$67.4438	$67.44	$67.45	$67.40
Purchase #5	$63.97	3.678%	$66.3228	$66.32	$66.30	$66.30
Purchase #6	$228.35	5.184%	$240.1877	$240.19	$240.20	$240.20
Purchase #7	$43.78	10.701%	$48.4649	$48.46	$48.45	$48.50
7 purchase totals =	$842.04		$890.9466	$890.93	$890.90	$891.00