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	$9.77	13.121%	$11.0519	$11.05	$11.05	$11.10
Purchase #2	$240.90	7.665%	$259.365	$259.37	$259.35	$259.40
Purchase #3	$43.78	13.773%	$49.8098	$49.81	$49.80	$49.80
Purchase #4	$245.43	6.755%	$262.0088	$262.01	$262.00	$262.00
Purchase #5	$70.43	11.403%	$78.4611	$78.46	$78.45	$78.50
Purchase #6	$20.32	6.410%	$21.6225	$21.62	$21.60	$21.60
Purchase #7	$130.66	12.705%	$147.2604	$147.26	$147.25	$147.30
7 purchase totals =	$761.29		$829.5795	$829.58	$829.50	$829.70