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	$123.31	10.505%	$136.2637	$136.26	$136.25	$136.30
Purchase #2	$83.73	7.175%	$89.7376	$89.74	$89.75	$89.70
Purchase #3	$23.96	8.204%	$25.9257	$25.93	$25.95	$25.90
Purchase #4	$155.74	3.301%	$160.881	$160.88	$160.90	$160.90
Purchase #5	$122.65	7.182%	$131.4587	$131.46	$131.45	$131.50
Purchase #6	$217.42	7.410%	$233.5308	$233.53	$233.55	$233.50
Purchase #7	$71.83	13.175%	$81.2936	$81.29	$81.30	$81.30
7 purchase totals =	$798.64		$859.0911	$859.09	$859.15	$859.10