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	$11.83	5.361%	$12.4642	$12.46	$12.45	$12.50
Purchase #2	$66.28	9.338%	$72.4692	$72.47	$72.45	$72.50
Purchase #3	$177.73	6.247%	$188.8328	$188.83	$188.85	$188.80
Purchase #4	$109.29	3.254%	$112.8463	$112.85	$112.85	$112.80
Purchase #5	$124.83	4.312%	$130.2127	$130.21	$130.20	$130.20
Purchase #6	$80.34	6.384%	$85.4689	$85.47	$85.45	$85.50
Purchase #7	$182.78	13.343%	$207.1683	$207.17	$207.15	$207.20
7 purchase totals =	$753.08		$809.4624	$809.46	$809.40	$809.50