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	$23.52	3.599%	$24.3665	$24.37	$24.35	$24.40
Purchase #2	$166.58	13.382%	$188.8717	$188.87	$188.85	$188.90
Purchase #3	$218.56	6.837%	$233.5029	$233.50	$233.50	$233.50
Purchase #4	$100.72	8.618%	$109.4	$109.40	$109.40	$109.40
Purchase #5	$224.93	11.681%	$251.2041	$251.20	$251.20	$251.20
Purchase #6	$73.65	13.366%	$83.4941	$83.49	$83.50	$83.50
Purchase #7	$117.73	6.720%	$125.6415	$125.64	$125.65	$125.60
7 purchase totals =	$925.69		$1,016.4808	$1,016.47	$1,016.45	$1,016.50