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	$104.87	3.165%	$108.1891	$108.19	$108.20	$108.20
Purchase #2	$7.81	8.184%	$8.4492	$8.45	$8.45	$8.40
Purchase #3	$87.39	13.466%	$99.1579	$99.16	$99.15	$99.20
Purchase #4	$140.46	10.735%	$155.5384	$155.54	$155.55	$155.50
Purchase #5	$241.65	5.653%	$255.3105	$255.31	$255.30	$255.30
Purchase #6	$203.63	7.282%	$218.4583	$218.46	$218.45	$218.50
Purchase #7	$50.90	5.835%	$53.87	$53.87	$53.85	$53.90
7 purchase totals =	$836.71		$898.9734	$898.98	$898.95	$899.00