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	$99.61	11.675%	$111.2395	$111.24	$111.25	$111.20
Purchase #2	$238.88	7.288%	$256.2896	$256.29	$256.30	$256.30
Purchase #3	$215.93	12.143%	$242.1504	$242.15	$242.15	$242.20
Purchase #4	$83.80	5.264%	$88.2112	$88.21	$88.20	$88.20
Purchase #5	$98.95	13.783%	$112.5883	$112.59	$112.60	$112.60
Purchase #6	$96.32	9.291%	$105.2691	$105.27	$105.25	$105.30
Purchase #7	$115.92	13.823%	$131.9436	$131.94	$131.95	$131.90
7 purchase totals =	$949.41		$1,047.6917	$1,047.69	$1,047.70	$1,047.70