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	$177.83	3.298%	$183.6948	$183.69	$183.70	$183.70
Purchase #2	$170.30	11.230%	$189.4247	$189.42	$189.40	$189.40
Purchase #3	$96.35	13.471%	$109.3293	$109.33	$109.35	$109.30
Purchase #4	$212.27	13.660%	$241.2661	$241.27	$241.25	$241.30
Purchase #5	$160.78	7.802%	$173.3241	$173.32	$173.30	$173.30
Purchase #6	$17.64	4.667%	$18.4633	$18.46	$18.45	$18.50
Purchase #7	$25.57	6.801%	$27.309	$27.31	$27.30	$27.30
7 purchase totals =	$860.74		$942.8113	$942.80	$942.75	$942.80