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	$80.60	7.788%	$86.8771	$86.88	$86.90	$86.90
Purchase #2	$243.81	9.161%	$266.1454	$266.15	$266.15	$266.10
Purchase #3	$234.89	8.857%	$255.6942	$255.69	$255.70	$255.70
Purchase #4	$144.95	10.317%	$159.9045	$159.90	$159.90	$159.90
Purchase #5	$249.32	7.333%	$267.6026	$267.60	$267.60	$267.60
Purchase #6	$56.45	10.457%	$62.353	$62.35	$62.35	$62.40
Purchase #7	$120.78	8.613%	$131.1828	$131.18	$131.20	$131.20
7 purchase totals =	$1,130.80		$1,229.7596	$1,229.75	$1,229.80	$1,229.80