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	$225.40	9.292%	$246.3442	$246.34	$246.35	$246.30
Purchase #2	$56.75	10.380%	$62.6407	$62.64	$62.65	$62.60
Purchase #3	$162.28	11.582%	$181.0753	$181.08	$181.10	$181.10
Purchase #4	$90.26	11.869%	$100.973	$100.97	$100.95	$101.00
Purchase #5	$99.86	12.394%	$112.2366	$112.24	$112.25	$112.20
Purchase #6	$62.79	7.493%	$67.4949	$67.49	$67.50	$67.50
Purchase #7	$34.72	13.471%	$39.3971	$39.40	$39.40	$39.40
7 purchase totals =	$732.06		$810.1618	$810.16	$810.20	$810.10