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	$224.37	6.488%	$238.9271	$238.93	$238.95	$238.90
Purchase #2	$43.71	12.636%	$49.2332	$49.23	$49.25	$49.20
Purchase #3	$100.83	9.400%	$110.308	$110.31	$110.30	$110.30
Purchase #4	$149.72	6.123%	$158.8874	$158.89	$158.90	$158.90
Purchase #5	$189.61	4.149%	$197.4769	$197.48	$197.50	$197.50
Purchase #6	$15.86	13.629%	$18.0216	$18.02	$18.00	$18.00
Purchase #7	$95.81	12.296%	$107.5908	$107.59	$107.60	$107.60
7 purchase totals =	$819.91		$880.4450	$880.45	$880.50	$880.40