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	$132.54	11.591%	$147.9027	$147.90	$147.90	$147.90
Purchase #2	$38.83	10.263%	$42.8151	$42.82	$42.80	$42.80
Purchase #3	$174.58	12.810%	$196.9437	$196.94	$196.95	$196.90
Purchase #4	$164.71	5.594%	$173.9239	$173.92	$173.90	$173.90
Purchase #5	$43.76	9.570%	$47.9478	$47.95	$47.95	$47.90
Purchase #6	$59.35	11.275%	$66.0417	$66.04	$66.05	$66.00
Purchase #7	$129.55	12.323%	$145.5144	$145.51	$145.50	$145.50
7 purchase totals =	$743.32		$821.0893	$821.08	$821.05	$820.90