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	$116.25	13.212%	$131.609	$131.61	$131.60	$131.60
Purchase #2	$11.60	12.786%	$13.0832	$13.08	$13.10	$13.10
Purchase #3	$250.46	13.141%	$283.3729	$283.37	$283.35	$283.40
Purchase #4	$62.41	6.312%	$66.3493	$66.35	$66.35	$66.30
Purchase #5	$90.93	13.817%	$103.4938	$103.49	$103.50	$103.50
Purchase #6	$79.71	3.582%	$82.5652	$82.57	$82.55	$82.60
Purchase #7	$116.60	12.264%	$130.8998	$130.90	$130.90	$130.90
7 purchase totals =	$727.96		$811.3732	$811.37	$811.35	$811.40