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	$245.82	13.543%	$279.1114	$279.11	$279.10	$279.10
Purchase #2	$168.70	11.351%	$187.8491	$187.85	$187.85	$187.80
Purchase #3	$41.84	12.541%	$47.0872	$47.09	$47.10	$47.10
Purchase #4	$111.90	5.157%	$117.6707	$117.67	$117.65	$117.70
Purchase #5	$90.51	6.393%	$96.2963	$96.30	$96.30	$96.30
Purchase #6	$92.69	11.262%	$103.1287	$103.13	$103.15	$103.10
Purchase #7	$238.25	11.560%	$265.7917	$265.79	$265.80	$265.80
7 purchase totals =	$989.71		$1,096.9351	$1,096.94	$1,096.95	$1,096.90