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	$81.77	5.757%	$86.4775	$86.48	$86.50	$86.50
Purchase #2	$77.74	13.379%	$88.1408	$88.14	$88.15	$88.10
Purchase #3	$249.55	4.172%	$259.9612	$259.96	$259.95	$260.00
Purchase #4	$107.53	3.658%	$111.4634	$111.46	$111.45	$111.50
Purchase #5	$106.77	11.853%	$119.4254	$119.43	$119.45	$119.40
Purchase #6	$78.25	11.667%	$87.3794	$87.38	$87.40	$87.40
Purchase #7	$163.66	6.172%	$173.7611	$173.76	$173.75	$173.80
7 purchase totals =	$865.27		$926.6088	$926.61	$926.65	$926.70