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	$27.28	7.812%	$29.4111	$29.41	$29.40	$29.40
Purchase #2	$50.40	10.447%	$55.6653	$55.67	$55.65	$55.70
Purchase #3	$7.83	10.509%	$8.6529	$8.65	$8.65	$8.70
Purchase #4	$57.69	8.204%	$62.4229	$62.42	$62.40	$62.40
Purchase #5	$169.29	11.362%	$188.5247	$188.52	$188.50	$188.50
Purchase #6	$66.39	6.522%	$70.72	$70.72	$70.70	$70.70
Purchase #7	$219.41	4.142%	$228.498	$228.50	$228.50	$228.50
7 purchase totals =	$598.29		$643.8949	$643.89	$643.80	$643.90