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	$45.83	6.547%	$48.8305	$48.83	$48.85	$48.80
Purchase #2	$83.72	4.458%	$87.4522	$87.45	$87.45	$87.50
Purchase #3	$223.66	11.609%	$249.6247	$249.62	$249.60	$249.60
Purchase #4	$150.64	6.593%	$160.5717	$160.57	$160.55	$160.60
Purchase #5	$103.87	6.750%	$110.8812	$110.88	$110.90	$110.90
Purchase #6	$234.44	13.585%	$266.2887	$266.29	$266.30	$266.30
Purchase #7	$19.46	12.784%	$21.9478	$21.95	$21.95	$21.90
7 purchase totals =	$861.62		$945.5968	$945.59	$945.60	$945.60