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	$130.88	10.443%	$144.5478	$144.55	$144.55	$144.50
Purchase #2	$213.28	4.212%	$222.2634	$222.26	$222.25	$222.30
Purchase #3	$101.43	10.379%	$111.9574	$111.96	$111.95	$112.00
Purchase #4	$80.75	9.794%	$88.6587	$88.66	$88.65	$88.70
Purchase #5	$76.35	4.836%	$80.0423	$80.04	$80.05	$80.00
Purchase #6	$103.45	7.644%	$111.3577	$111.36	$111.35	$111.40
Purchase #7	$232.38	3.492%	$240.4947	$240.49	$240.50	$240.50
7 purchase totals =	$938.52		$999.3220	$999.32	$999.30	$999.40