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	$47.58	6.843%	$50.8359	$50.84	$50.85	$50.80
Purchase #2	$70.31	3.801%	$72.9825	$72.98	$73.00	$73.00
Purchase #3	$113.29	13.333%	$128.395	$128.40	$128.40	$128.40
Purchase #4	$24.47	10.209%	$26.9681	$26.97	$26.95	$27.00
Purchase #5	$103.52	7.640%	$111.4289	$111.43	$111.45	$111.40
Purchase #6	$59.70	5.236%	$62.8259	$62.83	$62.85	$62.80
Purchase #7	$141.61	11.292%	$157.6006	$157.60	$157.60	$157.60
7 purchase totals =	$560.48		$611.0369	$611.05	$611.10	$611.00