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	$29.88	4.771%	$31.3056	$31.31	$31.30	$31.30
Purchase #2	$107.43	4.731%	$112.5125	$112.51	$112.50	$112.50
Purchase #3	$180.88	10.470%	$199.8181	$199.82	$199.80	$199.80
Purchase #4	$131.47	10.820%	$145.6951	$145.70	$145.70	$145.70
Purchase #5	$29.65	5.323%	$31.2283	$31.23	$31.25	$31.20
Purchase #6	$199.60	12.450%	$224.4502	$224.45	$224.45	$224.50
Purchase #7	$6.71	6.804%	$7.1665	$7.17	$7.15	$7.20
7 purchase totals =	$685.62		$752.1763	$752.19	$752.15	$752.20