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	$106.55	8.411%	$115.5119	$115.51	$115.50	$115.50
Purchase #2	$33.92	6.507%	$36.1272	$36.13	$36.15	$36.10
Purchase #3	$245.45	7.261%	$263.2721	$263.27	$263.25	$263.30
Purchase #4	$89.49	12.620%	$100.7836	$100.78	$100.80	$100.80
Purchase #5	$145.48	6.662%	$155.1719	$155.17	$155.15	$155.20
Purchase #6	$38.57	13.866%	$43.9181	$43.92	$43.90	$43.90
Purchase #7	$78.77	13.723%	$89.5796	$89.58	$89.60	$89.60
7 purchase totals =	$738.23		$804.3644	$804.36	$804.35	$804.40