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	$203.82	12.756%	$229.8193	$229.82	$229.80	$229.80
Purchase #2	$92.96	5.823%	$98.3731	$98.37	$98.35	$98.40
Purchase #3	$230.35	10.161%	$253.7559	$253.76	$253.75	$253.80
Purchase #4	$220.50	6.639%	$235.139	$235.14	$235.15	$235.10
Purchase #5	$30.36	3.152%	$31.3169	$31.32	$31.30	$31.30
Purchase #6	$31.26	6.857%	$33.4035	$33.40	$33.40	$33.40
Purchase #7	$237.47	9.417%	$259.8325	$259.83	$259.85	$259.80
7 purchase totals =	$1,046.72		$1,141.6402	$1,141.64	$1,141.60	$1,141.60