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	$20.92	12.584%	$23.5526	$23.55	$23.55	$23.60
Purchase #2	$98.36	9.617%	$107.8193	$107.82	$107.80	$107.80
Purchase #3	$190.59	7.633%	$205.1377	$205.14	$205.15	$205.10
Purchase #4	$171.55	11.245%	$190.8408	$190.84	$190.85	$190.80
Purchase #5	$59.78	13.432%	$67.8096	$67.81	$67.80	$67.80
Purchase #6	$179.85	9.193%	$196.3836	$196.38	$196.40	$196.40
Purchase #7	$9.37	10.182%	$10.3241	$10.32	$10.30	$10.30
7 purchase totals =	$730.42		$801.8677	$801.86	$801.85	$801.80