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	$9.55	5.455%	$10.071	$10.07	$10.05	$10.10
Purchase #2	$80.84	10.512%	$89.3379	$89.34	$89.35	$89.30
Purchase #3	$248.72	12.358%	$279.4568	$279.46	$279.45	$279.50
Purchase #4	$142.62	9.707%	$156.4641	$156.46	$156.45	$156.50
Purchase #5	$215.78	11.696%	$241.0176	$241.02	$241.00	$241.00
Purchase #6	$192.64	6.337%	$204.8476	$204.85	$204.85	$204.80
Purchase #7	$144.28	5.518%	$152.2414	$152.24	$152.25	$152.20
7 purchase totals =	$1,034.43		$1,133.4364	$1,133.44	$1,133.40	$1,133.40