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	$144.31	11.284%	$160.5939	$160.59	$160.60	$160.60
Purchase #2	$111.42	7.789%	$120.0985	$120.10	$120.10	$120.10
Purchase #3	$38.36	4.799%	$40.2009	$40.20	$40.20	$40.20
Purchase #4	$11.93	12.215%	$13.3872	$13.39	$13.40	$13.40
Purchase #5	$197.33	4.304%	$205.8231	$205.82	$205.80	$205.80
Purchase #6	$130.97	6.517%	$139.5053	$139.51	$139.50	$139.50
Purchase #7	$35.70	10.399%	$39.4124	$39.41	$39.40	$39.40
7 purchase totals =	$670.02		$719.0213	$719.02	$719.00	$719.00