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	$84.65	5.820%	$89.5766	$89.58	$89.60	$89.60
Purchase #2	$95.47	8.388%	$103.478	$103.48	$103.50	$103.50
Purchase #3	$203.81	4.308%	$212.5901	$212.59	$212.60	$212.60
Purchase #4	$82.34	12.604%	$92.7181	$92.72	$92.70	$92.70
Purchase #5	$166.75	10.185%	$183.7335	$183.73	$183.75	$183.70
Purchase #6	$120.32	13.617%	$136.704	$136.70	$136.70	$136.70
Purchase #7	$161.28	6.346%	$171.5148	$171.51	$171.50	$171.50
7 purchase totals =	$914.62		$990.3151	$990.31	$990.35	$990.30