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	$139.42	13.718%	$158.5456	$158.55	$158.55	$158.50
Purchase #2	$224.78	10.374%	$248.0987	$248.10	$248.10	$248.10
Purchase #3	$30.45	3.476%	$31.5084	$31.51	$31.50	$31.50
Purchase #4	$141.89	7.538%	$152.5857	$152.59	$152.60	$152.60
Purchase #5	$15.48	5.211%	$16.2867	$16.29	$16.30	$16.30
Purchase #6	$119.96	7.218%	$128.6187	$128.62	$128.60	$128.60
Purchase #7	$33.80	12.833%	$38.1376	$38.14	$38.15	$38.10
7 purchase totals =	$705.78		$773.7814	$773.80	$773.80	$773.70