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	$240.33	6.472%	$255.8842	$255.88	$255.90	$255.90
Purchase #2	$204.73	5.465%	$215.9185	$215.92	$215.90	$215.90
Purchase #3	$149.60	4.231%	$155.9296	$155.93	$155.95	$155.90
Purchase #4	$17.75	9.615%	$19.4567	$19.46	$19.45	$19.50
Purchase #5	$38.99	11.352%	$43.4161	$43.42	$43.40	$43.40
Purchase #6	$45.46	11.465%	$50.672	$50.67	$50.65	$50.70
Purchase #7	$63.85	4.527%	$66.7405	$66.74	$66.75	$66.70
7 purchase totals =	$760.71		$808.0176	$808.02	$808.00	$808.00