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	$238.95	4.569%	$249.8676	$249.87	$249.85	$249.90
Purchase #2	$170.94	5.632%	$180.5673	$180.57	$180.55	$180.60
Purchase #3	$109.94	12.137%	$123.2834	$123.28	$123.30	$123.30
Purchase #4	$45.35	12.564%	$51.0478	$51.05	$51.05	$51.00
Purchase #5	$83.39	7.115%	$89.3232	$89.32	$89.30	$89.30
Purchase #6	$231.29	13.240%	$261.9128	$261.91	$261.90	$261.90
Purchase #7	$25.72	12.399%	$28.909	$28.91	$28.90	$28.90
7 purchase totals =	$905.58		$984.9111	$984.91	$984.85	$984.90