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	$28.35	11.868%	$31.7146	$31.71	$31.70	$31.70
Purchase #2	$156.33	10.739%	$173.1183	$173.12	$173.10	$173.10
Purchase #3	$177.35	5.854%	$187.7321	$187.73	$187.75	$187.70
Purchase #4	$101.30	9.622%	$111.0471	$111.05	$111.05	$111.00
Purchase #5	$181.46	8.235%	$196.4032	$196.40	$196.40	$196.40
Purchase #6	$132.67	8.418%	$143.8382	$143.84	$143.85	$143.80
Purchase #7	$242.77	9.504%	$265.8429	$265.84	$265.85	$265.80
7 purchase totals =	$1,020.23		$1,109.6964	$1,109.69	$1,109.70	$1,109.50