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	$47.35	11.640%	$52.8615	$52.86	$52.85	$52.90
Purchase #2	$83.37	10.512%	$92.1339	$92.13	$92.15	$92.10
Purchase #3	$144.87	3.260%	$149.5928	$149.59	$149.60	$149.60
Purchase #4	$20.79	11.105%	$23.0987	$23.10	$23.10	$23.10
Purchase #5	$83.49	3.691%	$86.5716	$86.57	$86.55	$86.60
Purchase #6	$42.32	7.318%	$45.417	$45.42	$45.40	$45.40
Purchase #7	$179.45	5.536%	$189.3844	$189.38	$189.40	$189.40
7 purchase totals =	$601.64		$639.0599	$639.05	$639.05	$639.10