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	$233.35	9.867%	$256.3746	$256.37	$256.35	$256.40
Purchase #2	$118.54	6.550%	$126.3044	$126.30	$126.30	$126.30
Purchase #3	$143.57	10.299%	$158.3563	$158.36	$158.35	$158.40
Purchase #4	$194.57	5.696%	$205.6527	$205.65	$205.65	$205.70
Purchase #5	$132.95	6.716%	$141.8789	$141.88	$141.90	$141.90
Purchase #6	$82.97	3.552%	$85.9171	$85.92	$85.90	$85.90
Purchase #7	$38.25	12.208%	$42.9196	$42.92	$42.90	$42.90
7 purchase totals =	$944.20		$1,017.4036	$1,017.40	$1,017.35	$1,017.50