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	$5.96	10.561%	$6.5894	$6.59	$6.60	$6.60
Purchase #2	$43.83	4.753%	$45.9132	$45.91	$45.90	$45.90
Purchase #3	$62.56	13.498%	$71.0043	$71.00	$71.00	$71.00
Purchase #4	$12.92	11.466%	$14.4014	$14.40	$14.40	$14.40
Purchase #5	$167.45	8.285%	$181.3232	$181.32	$181.30	$181.30
Purchase #6	$37.60	6.193%	$39.9286	$39.93	$39.95	$39.90
Purchase #7	$59.99	8.520%	$65.1011	$65.10	$65.10	$65.10
7 purchase totals =	$390.31		$424.2612	$424.25	$424.25	$424.20