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	$99.55	6.295%	$105.8167	$105.82	$105.80	$105.80
Purchase #2	$213.71	12.509%	$240.443	$240.44	$240.45	$240.40
Purchase #3	$221.86	3.783%	$230.253	$230.25	$230.25	$230.30
Purchase #4	$106.59	4.832%	$111.7404	$111.74	$111.75	$111.70
Purchase #5	$94.52	9.600%	$103.5939	$103.59	$103.60	$103.60
Purchase #6	$159.84	7.154%	$171.275	$171.28	$171.30	$171.30
Purchase #7	$5.33	5.383%	$5.6169	$5.62	$5.60	$5.60
7 purchase totals =	$901.40		$968.7389	$968.74	$968.75	$968.70