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	$24.72	10.564%	$27.3314	$27.33	$27.35	$27.30
Purchase #2	$230.44	5.639%	$243.4345	$243.43	$243.45	$243.40
Purchase #3	$215.25	7.645%	$231.7059	$231.71	$231.70	$231.70
Purchase #4	$20.42	4.719%	$21.3836	$21.38	$21.40	$21.40
Purchase #5	$156.87	13.564%	$178.1478	$178.15	$178.15	$178.10
Purchase #6	$108.79	9.871%	$119.5287	$119.53	$119.55	$119.50
Purchase #7	$176.29	6.667%	$188.0433	$188.04	$188.05	$188.00
7 purchase totals =	$932.78		$1,009.5752	$1,009.57	$1,009.65	$1,009.40