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	$25.92	8.678%	$28.1693	$28.17	$28.15	$28.20
Purchase #2	$80.48	10.298%	$88.7678	$88.77	$88.75	$88.80
Purchase #3	$82.94	4.540%	$86.7055	$86.71	$86.70	$86.70
Purchase #4	$78.95	4.306%	$82.3496	$82.35	$82.35	$82.30
Purchase #5	$40.57	4.768%	$42.5044	$42.50	$42.50	$42.50
Purchase #6	$131.31	4.659%	$137.4277	$137.43	$137.45	$137.40
Purchase #7	$48.62	7.868%	$52.4454	$52.45	$52.45	$52.40
7 purchase totals =	$488.79		$518.3697	$518.38	$518.35	$518.30