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	$249.37	3.257%	$257.492	$257.49	$257.50	$257.50
Purchase #2	$160.46	6.811%	$171.3889	$171.39	$171.40	$171.40
Purchase #3	$42.49	8.609%	$46.148	$46.15	$46.15	$46.10
Purchase #4	$174.88	4.242%	$182.2984	$182.30	$182.30	$182.30
Purchase #5	$176.27	3.545%	$182.5188	$182.52	$182.50	$182.50
Purchase #6	$65.60	9.114%	$71.5788	$71.58	$71.60	$71.60
Purchase #7	$52.85	10.779%	$58.5467	$58.55	$58.55	$58.50
7 purchase totals =	$921.92		$969.9716	$969.98	$970.00	$969.90