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	$71.48	13.545%	$81.162	$81.16	$81.15	$81.20
Purchase #2	$242.60	6.799%	$259.0944	$259.09	$259.10	$259.10
Purchase #3	$42.49	12.444%	$47.7775	$47.78	$47.80	$47.80
Purchase #4	$179.51	3.578%	$185.9329	$185.93	$185.95	$185.90
Purchase #5	$102.83	13.170%	$116.3727	$116.37	$116.35	$116.40
Purchase #6	$118.59	7.521%	$127.5092	$127.51	$127.50	$127.50
Purchase #7	$123.96	6.540%	$132.067	$132.07	$132.05	$132.10
7 purchase totals =	$881.46		$949.9157	$949.91	$949.90	$950.00