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	$24.39	3.163%	$25.1615	$25.16	$25.15	$25.20
Purchase #2	$123.94	6.482%	$131.9738	$131.97	$131.95	$132.00
Purchase #3	$161.95	3.432%	$167.5081	$167.51	$167.50	$167.50
Purchase #4	$35.41	4.571%	$37.0286	$37.03	$37.05	$37.00
Purchase #5	$48.69	11.785%	$54.4281	$54.43	$54.45	$54.40
Purchase #6	$144.61	8.275%	$156.5765	$156.58	$156.60	$156.60
Purchase #7	$104.86	11.855%	$117.2912	$117.29	$117.30	$117.30
7 purchase totals =	$643.85		$689.9678	$689.97	$690.00	$690.00