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	$10.84	5.371%	$11.4222	$11.42	$11.40	$11.40
Purchase #2	$19.60	3.332%	$20.2531	$20.25	$20.25	$20.30
Purchase #3	$9.56	13.259%	$10.8276	$10.83	$10.85	$10.80
Purchase #4	$161.27	9.442%	$176.4971	$176.50	$176.50	$176.50
Purchase #5	$104.71	11.571%	$116.826	$116.83	$116.85	$116.80
Purchase #6	$234.69	12.649%	$264.3759	$264.38	$264.40	$264.40
Purchase #7	$185.46	7.350%	$199.0913	$199.09	$199.10	$199.10
7 purchase totals =	$726.13		$799.2932	$799.30	$799.35	$799.30