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	$98.44	9.228%	$107.524	$107.52	$107.50	$107.50
Purchase #2	$46.36	6.745%	$49.487	$49.49	$49.50	$49.50
Purchase #3	$74.57	8.171%	$80.6631	$80.66	$80.65	$80.70
Purchase #4	$126.70	13.175%	$143.3927	$143.39	$143.40	$143.40
Purchase #5	$152.90	12.141%	$171.4636	$171.46	$171.45	$171.50
Purchase #6	$78.93	9.460%	$86.3968	$86.40	$86.40	$86.40
Purchase #7	$10.41	11.523%	$11.6095	$11.61	$11.60	$11.60
7 purchase totals =	$588.31		$650.5367	$650.53	$650.50	$650.60