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	$239.46	8.643%	$260.1565	$260.16	$260.15	$260.20
Purchase #2	$117.90	4.553%	$123.268	$123.27	$123.25	$123.30
Purchase #3	$169.48	12.362%	$190.4311	$190.43	$190.45	$190.40
Purchase #4	$164.35	3.772%	$170.5493	$170.55	$170.55	$170.50
Purchase #5	$106.88	3.419%	$110.5342	$110.53	$110.55	$110.50
Purchase #6	$32.57	8.260%	$35.2603	$35.26	$35.25	$35.30
Purchase #7	$42.92	5.747%	$45.3866	$45.39	$45.40	$45.40
7 purchase totals =	$873.56		$935.5860	$935.59	$935.60	$935.60