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	$86.88	4.107%	$90.4482	$90.45	$90.45	$90.40
Purchase #2	$166.87	7.422%	$179.2551	$179.26	$179.25	$179.30
Purchase #3	$230.69	10.595%	$255.1316	$255.13	$255.15	$255.10
Purchase #4	$143.84	10.323%	$158.6886	$158.69	$158.70	$158.70
Purchase #5	$178.97	4.467%	$186.9646	$186.96	$186.95	$187.00
Purchase #6	$62.94	7.715%	$67.7958	$67.80	$67.80	$67.80
Purchase #7	$132.31	6.632%	$141.0848	$141.08	$141.10	$141.10
7 purchase totals =	$1,002.50		$1,079.3687	$1,079.37	$1,079.40	$1,079.40