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	$46.26	11.362%	$51.5161	$51.52	$51.50	$51.50
Purchase #2	$134.92	5.372%	$142.1679	$142.17	$142.15	$142.20
Purchase #3	$90.80	12.850%	$102.4678	$102.47	$102.45	$102.50
Purchase #4	$162.64	12.564%	$183.0741	$183.07	$183.05	$183.10
Purchase #5	$157.60	4.441%	$164.599	$164.60	$164.60	$164.60
Purchase #6	$128.32	9.839%	$140.9454	$140.95	$140.95	$140.90
Purchase #7	$53.70	7.278%	$57.6083	$57.61	$57.60	$57.60
7 purchase totals =	$774.24		$842.3786	$842.39	$842.30	$842.40