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	$13.34	3.477%	$13.8038	$13.80	$13.80	$13.80
Purchase #2	$46.28	10.385%	$51.0862	$51.09	$51.10	$51.10
Purchase #3	$234.32	10.269%	$258.3823	$258.38	$258.40	$258.40
Purchase #4	$219.56	5.132%	$230.8278	$230.83	$230.85	$230.80
Purchase #5	$166.60	6.600%	$177.5956	$177.60	$177.60	$177.60
Purchase #6	$238.34	13.488%	$270.4873	$270.49	$270.50	$270.50
Purchase #7	$56.52	5.350%	$59.5438	$59.54	$59.55	$59.50
7 purchase totals =	$974.96		$1,061.7268	$1,061.73	$1,061.80	$1,061.70