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	$191.85	6.283%	$203.9039	$203.90	$203.90	$203.90
Purchase #2	$235.98	5.166%	$248.1707	$248.17	$248.15	$248.20
Purchase #3	$90.62	10.714%	$100.329	$100.33	$100.35	$100.30
Purchase #4	$113.40	10.608%	$125.4295	$125.43	$125.45	$125.40
Purchase #5	$41.68	5.259%	$43.872	$43.87	$43.85	$43.90
Purchase #6	$140.78	8.757%	$153.1081	$153.11	$153.10	$153.10
Purchase #7	$104.60	4.704%	$109.5204	$109.52	$109.50	$109.50
7 purchase totals =	$918.91		$984.3336	$984.33	$984.30	$984.30