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	$106.80	12.874%	$120.5494	$120.55	$120.55	$120.50
Purchase #2	$127.86	5.149%	$134.4435	$134.44	$134.45	$134.40
Purchase #3	$164.63	12.471%	$185.161	$185.16	$185.15	$185.20
Purchase #4	$50.35	12.578%	$56.683	$56.68	$56.70	$56.70
Purchase #5	$29.82	10.134%	$32.842	$32.84	$32.85	$32.80
Purchase #6	$105.36	6.820%	$112.5456	$112.55	$112.55	$112.50
Purchase #7	$176.87	4.735%	$185.2448	$185.24	$185.25	$185.20
7 purchase totals =	$761.69		$827.4693	$827.46	$827.50	$827.30