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	$33.46	3.139%	$34.5103	$34.51	$34.50	$34.50
Purchase #2	$146.49	12.577%	$164.914	$164.91	$164.90	$164.90
Purchase #3	$154.30	6.758%	$164.7276	$164.73	$164.75	$164.70
Purchase #4	$197.68	7.672%	$212.846	$212.85	$212.85	$212.80
Purchase #5	$18.39	10.411%	$20.3046	$20.30	$20.30	$20.30
Purchase #6	$12.95	3.543%	$13.4088	$13.41	$13.40	$13.40
Purchase #7	$45.51	8.693%	$49.4662	$49.47	$49.45	$49.50
7 purchase totals =	$608.78		$660.1775	$660.18	$660.15	$660.10