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	$51.50	11.874%	$57.6151	$57.62	$57.60	$57.60
Purchase #2	$88.28	6.835%	$94.3139	$94.31	$94.30	$94.30
Purchase #3	$103.40	12.418%	$116.2402	$116.24	$116.25	$116.20
Purchase #4	$6.29	11.161%	$6.992	$6.99	$7.00	$7.00
Purchase #5	$59.54	9.288%	$65.0701	$65.07	$65.05	$65.10
Purchase #6	$224.47	10.222%	$247.4153	$247.42	$247.40	$247.40
Purchase #7	$73.57	12.713%	$82.923	$82.92	$82.90	$82.90
7 purchase totals =	$607.05		$670.5696	$670.57	$670.50	$670.50