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	$50.71	4.218%	$52.8489	$52.85	$52.85	$52.80
Purchase #2	$61.84	7.336%	$66.3766	$66.38	$66.40	$66.40
Purchase #3	$80.57	13.677%	$91.5896	$91.59	$91.60	$91.60
Purchase #4	$53.68	12.527%	$60.4045	$60.40	$60.40	$60.40
Purchase #5	$53.50	12.565%	$60.2223	$60.22	$60.20	$60.20
Purchase #6	$82.93	13.838%	$94.4059	$94.41	$94.40	$94.40
Purchase #7	$116.64	5.807%	$123.4133	$123.41	$123.40	$123.40
7 purchase totals =	$499.87		$549.2611	$549.26	$549.25	$549.20