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	$40.89	3.773%	$42.4328	$42.43	$42.45	$42.40
Purchase #2	$17.87	5.217%	$18.8023	$18.80	$18.80	$18.80
Purchase #3	$85.30	5.274%	$89.7987	$89.80	$89.80	$89.80
Purchase #4	$105.76	10.520%	$116.886	$116.89	$116.90	$116.90
Purchase #5	$237.92	9.348%	$260.1608	$260.16	$260.15	$260.20
Purchase #6	$90.63	9.357%	$99.1102	$99.11	$99.10	$99.10
Purchase #7	$96.62	5.484%	$101.9186	$101.92	$101.90	$101.90
7 purchase totals =	$674.99		$729.1094	$729.11	$729.10	$729.10