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	$170.78	9.159%	$186.4217	$186.42	$186.40	$186.40
Purchase #2	$191.76	7.331%	$205.8179	$205.82	$205.80	$205.80
Purchase #3	$106.73	5.726%	$112.8414	$112.84	$112.85	$112.80
Purchase #4	$41.39	5.867%	$43.8184	$43.82	$43.80	$43.80
Purchase #5	$60.39	9.721%	$66.2605	$66.26	$66.25	$66.30
Purchase #6	$87.74	13.564%	$99.6411	$99.64	$99.65	$99.60
Purchase #7	$39.54	4.747%	$41.417	$41.42	$41.40	$41.40
7 purchase totals =	$698.33		$756.2180	$756.22	$756.15	$756.10