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	$8.29	7.535%	$8.9147	$8.91	$8.90	$8.90
Purchase #2	$174.43	7.522%	$187.5506	$187.55	$187.55	$187.60
Purchase #3	$25.92	10.302%	$28.5903	$28.59	$28.60	$28.60
Purchase #4	$69.80	12.147%	$78.2786	$78.28	$78.30	$78.30
Purchase #5	$209.72	6.792%	$223.9642	$223.96	$223.95	$224.00
Purchase #6	$132.33	3.189%	$136.55	$136.55	$136.55	$136.60
Purchase #7	$247.61	3.106%	$255.3008	$255.30	$255.30	$255.30
7 purchase totals =	$868.10		$919.1492	$919.14	$919.15	$919.30