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	$100.28	12.681%	$112.9965	$113.00	$113.00	$113.00
Purchase #2	$44.85	7.753%	$48.3272	$48.33	$48.35	$48.30
Purchase #3	$56.98	4.464%	$59.5236	$59.52	$59.50	$59.50
Purchase #4	$206.37	4.176%	$214.988	$214.99	$215.00	$215.00
Purchase #5	$106.45	4.478%	$111.2168	$111.22	$111.20	$111.20
Purchase #6	$97.63	7.561%	$105.0118	$105.01	$105.00	$105.00
Purchase #7	$106.48	12.865%	$120.1787	$120.18	$120.20	$120.20
7 purchase totals =	$719.04		$772.2426	$772.25	$772.25	$772.20