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	$79.76	3.661%	$82.68	$82.68	$82.70	$82.70
Purchase #2	$99.95	3.277%	$103.2254	$103.23	$103.25	$103.20
Purchase #3	$122.55	7.422%	$131.6457	$131.65	$131.65	$131.60
Purchase #4	$35.33	10.381%	$38.9976	$39.00	$39.00	$39.00
Purchase #5	$173.45	8.111%	$187.5185	$187.52	$187.50	$187.50
Purchase #6	$184.48	8.149%	$199.5133	$199.51	$199.50	$199.50
Purchase #7	$223.72	13.522%	$253.9714	$253.97	$253.95	$254.00
7 purchase totals =	$919.24		$997.5519	$997.56	$997.55	$997.50