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	$82.51	10.745%	$91.3757	$91.38	$91.40	$91.40
Purchase #2	$240.47	13.659%	$273.3158	$273.32	$273.30	$273.30
Purchase #3	$180.60	12.733%	$203.5958	$203.60	$203.60	$203.60
Purchase #4	$16.38	10.660%	$18.1261	$18.13	$18.15	$18.10
Purchase #5	$128.72	8.822%	$140.0757	$140.08	$140.10	$140.10
Purchase #6	$136.30	12.329%	$153.1044	$153.10	$153.10	$153.10
Purchase #7	$139.85	10.312%	$154.2713	$154.27	$154.25	$154.30
7 purchase totals =	$924.83		$1,033.8648	$1,033.88	$1,033.90	$1,033.90