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	$27.46	13.652%	$31.2088	$31.21	$31.20	$31.20
Purchase #2	$175.51	7.377%	$188.4574	$188.46	$188.45	$188.50
Purchase #3	$226.27	13.189%	$256.1128	$256.11	$256.10	$256.10
Purchase #4	$231.84	10.277%	$255.6662	$255.67	$255.65	$255.70
Purchase #5	$101.81	4.718%	$106.6134	$106.61	$106.60	$106.60
Purchase #6	$114.86	4.781%	$120.3515	$120.35	$120.35	$120.40
Purchase #7	$99.40	9.671%	$109.013	$109.01	$109.00	$109.00
7 purchase totals =	$977.15		$1,067.4231	$1,067.42	$1,067.35	$1,067.50