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	$112.83	12.647%	$127.0996	$127.10	$127.10	$127.10
Purchase #2	$106.71	11.380%	$118.8536	$118.85	$118.85	$118.90
Purchase #3	$97.29	8.391%	$105.4536	$105.45	$105.45	$105.50
Purchase #4	$147.69	12.789%	$166.5781	$166.58	$166.60	$166.60
Purchase #5	$18.46	13.832%	$21.0134	$21.01	$21.00	$21.00
Purchase #6	$245.43	10.105%	$270.2307	$270.23	$270.25	$270.20
Purchase #7	$37.69	9.651%	$41.3275	$41.33	$41.35	$41.30
7 purchase totals =	$766.10		$850.5565	$850.55	$850.60	$850.60