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	$23.95	4.453%	$25.0165	$25.02	$25.00	$25.00
Purchase #2	$222.30	3.739%	$230.6118	$230.61	$230.60	$230.60
Purchase #3	$144.91	6.249%	$153.9654	$153.97	$153.95	$154.00
Purchase #4	$197.90	12.186%	$222.0161	$222.02	$222.00	$222.00
Purchase #5	$250.97	11.777%	$280.5267	$280.53	$280.55	$280.50
Purchase #6	$180.51	8.540%	$195.9256	$195.93	$195.95	$195.90
Purchase #7	$69.78	12.222%	$78.3085	$78.31	$78.30	$78.30
7 purchase totals =	$1,090.32		$1,186.3706	$1,186.39	$1,186.35	$1,186.30