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	$69.49	13.395%	$78.7982	$78.80	$78.80	$78.80
Purchase #2	$122.82	13.182%	$139.0101	$139.01	$139.00	$139.00
Purchase #3	$136.64	11.405%	$152.2238	$152.22	$152.20	$152.20
Purchase #4	$55.88	10.402%	$61.6926	$61.69	$61.70	$61.70
Purchase #5	$124.35	11.311%	$138.4152	$138.42	$138.40	$138.40
Purchase #6	$227.43	8.487%	$246.732	$246.73	$246.75	$246.70
Purchase #7	$144.71	13.691%	$164.5222	$164.52	$164.50	$164.50
7 purchase totals =	$881.32		$981.3941	$981.39	$981.35	$981.30